SOVIET ATOMIC ENERGY VOL. 44, NO. 1

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• Publication Date: July 1, 1978
• Content Type: REPORT

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Russian Original Vol. 44, No. '1, January, 1978
July, 1978
SATEAZ 44(1) 1-110 (1978)
? SOVIET
ATOMIC
ENERGY
ATOMHAR 3HEKHR
(ATOMNAYA ENERGIYA)
TRANSLATED FROM RUSSIAN,
CONSULTANTS'BUREAU NEW YORK
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SOVIET Soviet Atomic Energy is a cover-to-cover translation of Atomnaya
Energiya, a publication of the Academy of Sciences of the USSR.
ATOMIC
ENERGY
Soviet.. Atomic Energy is abstracted or in-
dexed in Applied Mechanics Reviews, Chem-
ical Abstracts, Engineering Index, INSPEC?
Physics Abstracts and Electrical and Elec-
tronics Abstracts, Current Contents, and
Nuclear Science Abstracts.
An agreement with the Copyright Agency of the USSR (VAAP)
makes available both advance copies of the Russian journal and
original glossy photographs and artwork. This serves to decrease
the necessary time lag between publication of the original and
publication of the translation and helps to improve the quality
of the latter. The translation began with the first issue of the
Russian journal.
Editorial Board of Atomnaya Energiya:
Editor: 0. D. Kazachkovskii
Associate 'Editor: N. A. Vlasov
A. A. Bochvar
N. A. Dollezhal'
V. S. Fursov.
I. N. Golovin
V. F. Kalinin
A. K. Krasin
V. V. Matveev
M. G. Meshcheryakov
V. B. Shevchenko
V.1. Smirnov
A. P. Zefirov
Copyright C) 1978, Plenum Publishing Corporation. Soviet Atomic Energy partici-
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SOVIET ATOMIC ENERGY
A translation of Atomnaya Energiya
July, 1978
Volume 44, Number 1
January, 1978
ARTICLES
CONTENTS
Engl./Russ.
Sixty Years of Soviet Science ? A. P. Aleksandrov
1
5
The Birth of Nuclear Power ? N. A. Dollezhal,
10
14
The Past Becomes History ? L. M. Nemenov
13
17
Spontaneous Fission of Heavy Nuclei ? K. A. Petrzhak and G. N. Flerov
18
22
Isomers in the Millisecond Region ? A. P. Klyucharev, V. V. Remaev,
and Yu. N. Rakivnenko
32
36
Annihilation as an Energy Source ? N. A. Vlasov
40
45
Thirty Years of Work at the First Nuclear Laboratory at Dubna ? V. P. Dzhelepov
and L. I. Lapidus
46
50
Thermalization of Neutrons ? V. I. Mostovoi
61
65
Shell and Isotope Effects in Neutron?Nucleus Interactions ? M. V. Pasechnik
67
70
Research on Toroidal Plasma Confinement at the Kharkov Physicotechnical Institute
of the Academy of Sciences of the Ukranian SSR? V. T. Tolok
69
73
BOOK REVIEWS
V. L Bochenin. Radioisotope Techniques in the Analysis of Industrial Materials
? Reviewed by E. R. Kartashev .
79
82
DEPOSITED PAPERS
Optimization of Radiation Monitoring in Regions around Atomic Power Plants
? L. L Piskunov, V. M. Gushchin, and S. I. Treiger
80
83
Use of Channeling Method to Study Radiation Damage in Alkali-Halide Crystals
? E. T. Shipatov, A. S. Borovik, L. K. Mamaev, and V. S. Popov
81
84
Isotopic Anomalies of Xenon from Natural Nuclear Reactor (Deposited at Okhlo,
Gabon, Africa) ? Yu. A. Shukolyukov and Dang Vu Minh
81
84
y-Ray Albedo for Iron Plates ? V. I. Kulikov, K. K. Popkov, and I. N. Trofimov
?
82
85
LETTERS TO THE EDITOR
Control of Space?Time Distribution of Xenon in Nuclear Reactor ? T. S. Zaritskaya
and A. P. Rudik
84
86
Kinetics of Solution of Solid Sodium Hydroxide in Sodium ? F. A. Kozlov,
G. P. Sergeev, A. R. Sednev, and V. M. Makarov
87
88
Heat Strength of Graphite for Power Reactors ? Yu. S. Virgiliev ? ? ?
89
89
Calculation of Local Heat Fluxes in Circular Channel with Liquid Metal
? V. S. Sroelov and P. P. Bocharin
91
91
Effective Photon Attenuation Coefficients for Heterogeneous Media
? V. A. Artsybashev and E. P. Leman
94
93
BIRTHDAYS
Sixtieth Birthday of Evgenii Ivanovich Vorob'ev
97
95
CONFERENCES AND MEETINGS
Tenth World Power Engineering Congress ? Yu. I. Koryakin
100
97
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CONTENTS
(continued)
Engl./Russ.
Radiation Effects in Structural Materials of Fast Reactors ? V. N. Bykov
103
100
Fourth Session of Soviet?American Coordination Commission on Thermonuclear
Energy ? G. A. Eliseev
105
101
? Meeting of Technical Committee 45 of the International Electrotechnical Commission
on Nuclear Instrumentation ? L. G. Kiselev
107
102
? Symposium of American Electrochemical Society ? Yu. L Tisov, A. F. Kapustin,
and V. N. Smagin
109
104
The Russian press date (podpisa.no k pechati) of this issue was 12/28/1977.
Publication therefore did not occur prior to this date, but must be assumed
to have taken place reasonably soon thereafter.
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ARTICLES
SIXTY YEARS OF SOVIET SCIENCE*
A. P. Aleksandrov t
Atomic Energy in the USSR
An enormous revolution took place in physics at the start of the 20th century ? the special and general
theories of relativity of Einstein appeared and the principle of mass ?energy equivalence was established,
and the quantum theory introduced by Planck appeared.
Rutherford showed in an investigation of the scattering of a particles by atoms that a positively charged
nucleus exists in the atom and advanced the planetary theory of atomic structure, consisting of a positively
charged nucleus and external electrons revolving around the nucleus. This theory was attractive but internally
contradictory, since based on classical notions such an atom could not be stable. Bohr, who applied the quan-
tum ideas of Planck to the planetary atom theory, introducing his own brilliant postulates, removed the con-
tradictions and laid the foundation for the contemporary quantum theory of the atom.
Finally, in 1919 Rutherford, bombarding nitrogen atoms with a particles, produced nuclei of oxygen and
hydrogen as the result of the first artificial nuclear reaction performed. This accomplishment essentially
marked the beginning of a new direction in science ? nuclear physics.
Much research has followed that of Rutherford, including work in the Soviet Union. His method of in-
vestigating nuclear transformations by means of bombarding nuclei with high-energy particles of natural origin
and later artificially accelerated ones (evidently the first proposal in this direction was made by the Soviet
scientist L. V. Mysovskii in 1922) has been widely applied right up to the present time.
The 1930 papers of W. Bothe and H. Becker, in which the production of penetrating radiation was de-
tected upon the bombardment of light elements (e.g., beryllium) with a particles, are especially noteworthy.
It was initially supposed that these were a rays; however, in 1932 J. Chadwick in England showed that they
were uncharged particles with a mass equal to the mass of the proton. Thus, the neutron was discovered.
The discovery of the neutron began a new age in nuclear physics; there appeared a new projectile which could
not be repelled by the atomic nucleus, and its use promised completely new results.
The new situation in nuclear physics drew increased attention from Soviet scientists. The period of de-
velopment of the science had not been passed ? starting from 1932 the young I. V. Kurchatov, A . I. All-
khanov, and other scientists began to develop research in nuclear physics at the A. F. Ioffe Institute.
Research in the area of nuclear physics was being conducted still prior to this at the Radium Institute,
where they attempted to realize the idea of Mysovskii on artificially accelerated particles, but technical limi-
tations at the time did not allow them to do this.
The Kharkov Physicotechnical Institute (KFTI) was working in this direction. What was the state of
readiness of Soviet scientists for research in the field of nuclear physics? This is evident, e.g., from the
fact that the historic experiment of J. Cockcroft and E. Walton on the fission of lithium nuclei by protons,
carried out in April 1932 in England, was repeated at Kharkov by K. D. Sinel'nikov and Kurchatov in October
of the same year; it was necessary to create an accelerator in order to perform this experiment.
After a number of attempts at developing the idea of a cyclotron the large cyclotron of E. Lawrence at
Berkeley (U.S.A .) with a diameter of 700 mm for the poles was started up in 1932. The first small cyclotron
outside of Berkeley ? at the Leningrad Physicotechnical Institute (LFTI) in Kurchatov's laboratory ? was
started up in 1933.
In 1932 a decision was adopted to create at the Radium Institute a cyclotron with poles 1 m in diameter.
The cyclotron was started up in 1936. It was the first large cyclotron in Europe, and only in 1937 was the
*Complete text of an article published in: October and Science, Nauka, Moscow (1977).
t President of the USSR Academy of Sciences of the USSR.
Moscow. Translated from Atomnaya Energiya, Vol. 44, No. 1, pp. 5-14, January, 1978.
0038-531X/78/4401-0001$07.50 ?1978 Plenum Publishing Corporation
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cyclotron chamber at Berkeley replaced by a new one with poles about 1 m in diameter. In 1933 construction
was begun of the large LPTI cyclotron to upgrade the laboratory of I. V. Kurchatov and A . I. A likhanov. It
was almost finished before the war, but it proved possible to start it up only in 1946.
Electrostatic and cascade accelerators of various kinds were constructed at the KFTI and at the Lenin-
grad Polytechnical Institute, i.e., a fundamental experimental basis was then created for research in the
field of physics of the atomic nucleus. In addition to the physics of cosmic rays, the subjects of the interac-
tion of radiation with matter also began to be developed at the P. N. Lebedev Institute of Physics of the Acad-
emy of Sciences of the USSR.
The biggest new event was the discovery by Irene and Frederick Joliot-Curie of artificial radioactivity.
The work of E. Fermi on artificial radioactivity produced by neutrons slowed to thermal velocities opened up
new paths suitable for experiment. The radium?beryllium sources of neutrons prepared at the Radium
Institute, paraffin moderating units, and colleagues grabbing the irradiated targets and running headlong to
the counting apparatus in the laboratory of Kurchatov and A likhanov ? it was possible to witness such a scene
in the LFTI at that time.
Nuclear physics of the Soviet Union had emerged onto the level of world science. It began to bear fruit:
more than 100 papers were published by Soviet scientists during the period 1932-1935; important discoveries
were made. At the Lebedev Institute P. A. Cherenkov and S. I. Vavilov discovered the radiation which has
received the name Cherenkov (Cerenkov) radiation. Its nature was explained by I. E. Tamm and I. M. Franck,
who formulated a complete theory of this phenomenon. The discovery of Cerenkov radiation was later distin-
guished with the Nobel Prize. Kurchatov with his colleagues discovered nuclear isomerization, A likhanov
with his colleagues discovered the phenomenon of the ejection of electron? positron pairs by excited nuclei,
and L. A, Arts imovich and A likhanov proved conservation of momentum in connection with the annihilation of
a positron with an electron, and so on. Our country became one of the leading nations in the field of nuclear
physics.
Research was rapidly developed and moved to the leading edge in a number of other areas of physics in
which periods of growth deserving attention appeared. Thus, e.g., P. L. Kapitsa discovered the superfluidity
of helium, and L. D. landau gave it a quantum interpretation. Fundamental or first developments were car-
ried out in the Soviet Union in the fields of dielectric physics, semiconductor physics, luminescence, polymer
physics, and electron diffraction and microscopy, and in many other directions. The directions named by me
are only some examples and reflect the large contribution of research by Soviet scientists in the field of phy-
s ics .
This fine position of Soviet physics was due to a large extent to the very high level of the research of
Soviet theoreticians, Already in 1922 the Soviet theoretician A. A. Fridman (Friedmann) published the paper
"On the curvature of space." In this paper Friedmann showed that Einstein permitted a certain arbitrariness
when he sought a solution for the structure of space in a steady-state form. After discussion Einstein acknow-
ledged that the Friedmann solution was "a correct one and sheds new light." The contemporary notion of an
expanding universe was contained in the Friedmann solution, which was evaluated only following his death
after the redshift of spectral lines had been discovered. Such scientists as V. A. Fock, Ya. I. Frenkel',
and I. E. Tamm belonged to a small group of the leading theoretical physicists of the world. An uncommon
possession of mathematical tools was characteristic of Fock. He approached a problem rigorously, introducing
simplifications only where it was possible to prove their acceptability. Fock made an enormous contribution
to the development of various aspects of quantum mechanics: he generalized Schrtidinger's equations to the
case of a magnetic field, derived the scalar relativistic equations (the Klein? Fock equation), proved together
with M. Born the adiabatic theorem, worked out an exceptionally powerful method (the Hartree ?Fock method)
for the calculation of multielectron atomic and molecular systems, and developed the methods of quantum field
theory, second quantization, and quantum electrodynamics.
He was very resourceful: he did a lot on relativity theory, the diffraction and propagation of radio waves,
and even on logging theory.
The research of the remarkable theoretician Frenkel' had a completely different style. The basis of his
activity was an unusual physical problem-solving ability. Frenkel' drew on mathematics mainly for approxi-
mate estimates; an exceedingly clear physical idea was always of paramount importance to him. His credo
was :- "It is not necessary to search for the old in the new, but it is necessary to find the new in the old."
Frankel' brought an amazingly large number of new ideas into contemporary physics. He often advanced
them in sketchy form, so to speak, and some of them were retained in science without any connection with his
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name, which would succeed in evaporating. He created the principles of the quantum theory of metals, which
was developed further by F. Bloch and other authors. Frenkel' first treated the current in a metal as the
propagation of electron waves, which can be scattered by lattice irregularities, including thermal fluctuations
of the density. The principles of the contemporary physics of imperfect crystals were completely expounded
by Frenkel'. The concepts of vacancies, displaced atoms, and exitons were introduced by Frenkel'. He was
the first theoretician who decided to consider the physics of crystal impurities, and he was the first to intro-
duce the idea of near and distant order in condensed media, and so on. He was responsible for the first model
treatment of the atomic nucleus as a liquid drop. Frenkel' was the first to apply this model to the investiga
tion of nuclear fission. These ideas were later developed by Bohr and J. Wheeler.
Tamm, who worked at the Lebedev Institute in Moscow, was a constant participant in seminars at the
LPTI. His creative and unusual benevolent discussion of all research exerted an exceedingly stimulating
effect on all physicists who associated with him, both theoreticians and experimentalists. His research on
the scattering of y rays by electrons based on the quantum theory of light scattering in matter and the rela-
tivistic quantum theory of light scattering by electrons significantly developed the physical ideas in these
areas. His investigation touching on the nature of nuclear forces played a large role in the development of
contemporary views in this area.
One cannot overestimate the role also of those great physicists of the older generation, to a portion of
whom fell the honor and burden of organizing new scientific schools and the new Soviet physics. These were
physicists such as A. F. Ioffe, L. I. Mandel'shtam, N. D. Papalelcsi, G. S. Landsberg, P. N. robedev, P.
P. Lazarev, P. L. Kapitsa, I. I. Lukirskii, V. K. Frederiks, D. A. Rozhanskii, S. I. Vavilov, D. S.
Rozhdestvenskii, N. N. Semenov, and many others whose contribution to world science has been universally
recognized. The schools which they created determine the state of the Soviet physics of our time. We must
also count among them such remarkable physicists as L. D. landau, I. Ya. Pomeranchuk, M. A, 1.2 onto-
vich, N. N. Bogolyubov, M. A. Markov, Ya, B. Zel'dovich, and many other theoreticians, and such experi-
mental physicists as I. V. Kurchatov, L. A, Artsimovich, Yu, B. Khariton, P. P. Kobeko, A. M. Prok-
horov, N. G. Basov, and many, many others.
Approximately the same process took place in other areas of science.
We see in the example of physics that the system of science development created in the Soviet Union
after October and the system of training personnel and of education generally resulted in the advancement of
our science to the leading edge of world science. Any scientific problems are now within the power of our
country.
We will continue our discussion of this example, since the development of nuclear physics soon acquired
a vitally important meaning for the judgement of our Fatherland.
Intensive research on the physics of the atomic nucleus was continued in numerous laboratories of the
world. The discovery of new isotopes produced as the result of radioactive decay, the transmutationof certain
chemical elements to others, and the discovery of new types of nuclear reactions followed one after the other.
The ideas of the transformation of elements under the action of neutrons began to acquire universal recogni-
tion.
It is interesting that the great Austrian physicist L. Szilard described a hypothetical reactor with a chain
reaction by neutrons and introduced the concept of the critical mass and an estimate of it five years prior to
the discovery of uranium fission and before the start of the research of Fermi on the irradiation of various
elements by neutrons. He suggested using irradiation by neutrons in this reactor to produce the isotopes of
all the elements. This was the claim, and its publication occurred in 1932.
Already in the middle of the 1930s Joliot advanced the assumption in his Nobel speech that the energy of
the atomic nucleus would be used by mankind. Events ripened. At the end of 1938 0. Hahn and F. Strassmann
in Germany proved that an isotope of barium is produced upon the action of neutrons on uranium. This was
published at the start of January 1939. Two colleagues of N. Bohr ? 0. Frisch and L. Meitner ? advanced
the hypothesis that upon the capture of a neutron the uranium nucleus sometimes splits into two parts similar
in mass. If this is so, then the isotopes produced should be neutron-rich, and a process of the fission of the
uranium nucleus should be accompanied by the production of several neutrons. And this indicated that the
organization of a chain reaction of the fission of uranium by neutrons is conceivable. There followed literally
an explosion of papers on the investigation of fission. Already in the middle of January 1939 American,
Danish, and French papers in this field were published, and by the end of 1939 about one hundred papers, in-
cluding a number of Soviet ones, had already been published. It became clear towards the middle of 1939 that
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an enormous energy is released by the fission of a nucleus, that the fission is actually accompanied by the
emission of 2-3 neutrons, and that a chain reaction can be arranged both with slow and with fast neutrons.
Already at this time the cross sections of fission by fast and thermal neutrons were being refined, and
Zel'dovich and Khariton made correct estimates of the conditions for a fission chain reaction to arise. Soon
G. N. Flerov and K. A. Petrzhak at the laboratory of Kurchatov discovered the spontaneous fission of ura-
nium.
Towards the end of 1940 Kurchatov and Khariton developed a detailed plan of research for the accom-
plishment of a fission chain reaction with the suggestion to construct a device for the realization of a nuclear
chain reaction, i.e., a nuclear reactor. One might expect that with a good neutron modulator a nuclear reac-
tor based on natural uranium is possible. The construction of such a device was of doubly important signifi-
cance. In the first place, approaching the "critical conditions" gradually by increasing the amount of ura-
nium, it was possible to count on the possibility of a detailed investigation of the factors affecting the develop-
ment of a chain reaction and on the fact that it would be possible to control it, since according to theory the
chain reaction should develop or die down very slowly near the critical mass (the fact that delayed neutrons
exist in connection with the fission reaction, significantly facilitating the problem of regulation, was not
known at that time). In the second place, it was known at that time from a published paper of the Americans
E, McMillan and P. Abelson that the element with atomic number 93 is produced from the isotope 238U upon
Its capture of a neutron. This element was, according to McMillan, 13 radioactive with a half-life of 2.33 days.
This was the first discovery of an artificial transuranic element. Finally, after i3 decay the element 93
should have been transformed into the element with atomic number 94. McMillan and Abelson did not notice
the radioactivity of element 94, i.e., it was possible to assume that an element (stable or weakly radioactive,
long-lived) with atomic number 94 and atomic weight 239 will gradually accumulate in a nuclear reactor due
to the capture of part of the neutrons of 238U. It later received the name of plutonium.
This element should have been chemically different from uranium due to the different charge of its
nucleus, thanks to which it was possible to count on its chemical separation. One could assume that this ele-
ment would turn out to be fissionable both by slow and fast neutrons, so that it, just as 235U, was of parity.
All of these were only assumptions, and it was necessary to check them.
It should be said that the possibility of the realization of a reactor based on slow neutrons with natural
uranium, although very tempting, did not seem very sound, since it relied on calculations at the very limit.
Nuclear constants were known at that time with very poor accuracy, and the positive answer obtained
in the calculations was devoid of any margin for error, i.e., extremely unreliable. It was undoubtedly pos-
sible to accomplish reliably a chain reaction by using uranium in which the 238U content would be enhanced
with respect to natural uranium. However, the process of separation of the isotopes of uranium seemed pos-
sible but very expensive and complicated from an engineering point of view.
Kurchatov wrote a lecture in which he outlined the possible military and industrial value of the problem
of obtaining the energy of uranium fission, and he delivered it at the end of 1940 to the Presidium of the Acad-
emy of Sciences of the USSR. In this lecture Kurchatov suggested putting before the government the question
of assigning means to the uranium problem in connection with its exceptional significance. In November 1940
the uranium problem was discussed openly for the last time during this period at the All-Union Conference on
the Atomic Nucleus.
At this time a "strange," and later real, war was going on against Hitlerian Germany already for 1 year.
Many great physicists from countries where fascism was approved fled to England and the U.S.A. It seemed
natural that scientific publications were reduced in the European scientific journals ? this was the result of
the war. But all publications on fission, and later on isotope separation, began to be reduced in the American
journals in 1939 and finally disappeared in 1940. It was impossible to think that this was simply a general
curtailment of scientific activity, since scientific papers in other areas were published on their previous scales.
The authors who had worked earlier in the field of nuclear physics disappeared not only from the pages of the
scientific journals ? they also did not teach, and they did not give lectures. An unprecedented situation be-
came clear: an entire prominent division of science had evidently been made secret, possibly in connection
with its exceptional military significance.
Actually, it is now known that in 1939 a group of scientists lathe U.S.A. headed by Szilard, fearing that
scientific research on nuclear physics would help Nazi Germany produce an atomic weapon, agreed on his
initiative to curtail publications. They appealed to President Roosevelt through Einstein and communicated to
him concerning the possibility of a nuclear weapon and the fact that Nazi Germany was probably working on its
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realization, and they posed the question of the development of this research in the U.S.A. And this research
was expanded in large scale and under conditions of complete secrecy in specially created secret centers.
The scientists who had emigrated from fascist countries and the scientists of England and the U.S.A. began
working on the creation of the atomic bomb.
It was also obvious that research on a nuclear weapon was being conducted in Germany. All of this
caused great anxiety for the Soviet physicists. N. N. Semenov also appealed to government agencies with the
suggestion of expanding research on the atomic problem. However, soon Germany attacked the Soviet Union,
and a most brutal war began. The main nuclear laboratories ceased operation ? the evacuation of the Lenin-
grad, Kharkov, and Moscow scientific institutions began.
A significant portion of the scientists were in the army or were switched to research on military tasks.
In particular, Kurchatov and a large portion of the staff of his laboratory were engaged in research on anti-
mine protection of ships, which was conducted at the laboratory of the author.
Development of the Uranium Problem during the War
and during the Postwar Period
At this time there repeatedly arose the question: should not research on the uranium problem be revived?
Flerov, who served in the army, appealed to Ioffe, and then he sent a letter to Kurchatov with an urgent re-
quest not to postpone further the development of this research. He appealed with such a letter in the summer
of 1942 to the State Defense Committee, and soon he was summoned to Moscow for a lecture. It is obvious
that some information about research in Germany had also been obtained by our government.
And here at the most difficult period of the war in the fall of 1942 Kurchatov was summoned to Moscow,
and the first discussion occurred of the advisability of the development of research on the uranium problem.
M. G. Pervukhin and S. V. Kaftanov, whom the government had assigned to discuss this problem with compe-
tent individuals from among the scientists, arrived at the conviction that the research should begin.
They began to recall scientists from the army and from military research of different purpose, from
blockaded Leningrad and from the evacuation, and they sent them to the disposition of Kurchatov, who was
designated the scientific director of the problem. Nuclear research began gradually to redevelop at Kazan,
where the LPTI was located in the evacuation. At this time the battle of Stalingrad began, and the country
turned all its attention to it. Finally, a colossal victory was established, which everyone perceived as a
victorypredetermining the outcome of the war and which marked the turning point in it.
The situation improved in the country. The withdrawal of our forces ceased, and the need of further
evacuation passed. Industry which had been relocated in the east was now operating at full speed, and artillery,
tanks, and airplanes flowed to the front in a steady stream. Confident systematic preparation for total victory
was carried out.
The development of the machines intended for production after the end of the war gradually got underway
in the construction departments of industry. But more and more often threats of the use of a "superweapon"
reached our ears from Germany. It was known that Germany was attempting to take supplies of heavy water
out of Norway and that this convoy was blown up by the English.
It was impossible not to adopt countermeasures. On the instructions of the Central Committee of the
Party Kurchatov organized in Moscow at the start of 1943 a new scientific institution intended for the solution
of the uranium problem. The research was broad-based, and there even appeared the possibility of continuing
research on cosmic rays; the A likhanov brothers organized a mountain expedition into Armenia to A lagez.
The main directions of the research were determined to a significant extent still as before the war, but
now everything became broader and more specific.
The Central Committee of the Party demanded the expansion of research on a broader front. It was
necessary to duplicate the principal research for confidence in the results.
It was necessary to realize a chain reaction with natural uranium as far as possible. It was first of all
necessary to improve the theory of the reactor.
Then the young theoreticians I. Ya. Pomeranchuk and I. I. Gurevich with the assistance of Ya. B. Zel'-
dovich, who developed the theory of neutron moderation, also investigated while working out the reactor theory
the problem of the effect of the position of the uranium in the moderator on the neutron multiplication, which
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appeared decisive for reactors based on natural uranium. It was already known earlier from research on
artificial radioactivity that distributed and concentrated targets behave differently and that the absorption
cross section is less in thick targets.
It seemed that in the case of a reactor a uniform arrangement of uranium in the modulator and an
arrangement in the form of separate massive blocks separated by pure modulator differed significantly, with
the block arrangement giving a significant advantage in the neutron multiplication coefficient. Calculations
made with the block-effect taken into account, whose significance was quickly confirmed experimentally by
G. N. Flerov, V. A. Davidenko, and I. S. Panasyu.k, showed that a reactor with natural uranium and graphite
could be built with a sufficiently high purity of the graphite. The calculations provided the parameters of the
optimal lattice of reactors, i.e., the-basis for their construction.
A plan was entirely clear with regard to the problem, but it was incredibly difficult, espec tally unde r wartime
conditions, to begin intensified searches for uranium deposits and to organize the mining, to develop a tech-
nology for its extraction suitable for large-scale operations, and to work out the metallurgy of uranium, re-
fining methods, and methods of analysis unprecedented with respect to accuracy.
In addition to uranium, a moderator was necessary. This could be heavy water or graphite. But the
calculations were incomplete, and a reactor using graphite was likely not to work, especially if the graphite
were not very pure. This meant that it was necessary to organize the production of heavy water and to find
cheaper technology for its production and methods of analysis in addition to the well-known electrolysis meth-
od. Perhaps somewhere in nature conditions were produced under which the natural water contains more
deuterium?
It was necessary to organize expeditions and to examine the water of various isolated reservoirs.
The electrode graphite produced by industry was insufficiently pure. It was necessary to develop a new
technology and produce the purest graphite. And again analysis methods were needed which permit detecting
neutron-absorbing impurities in trace amounts. Academicians A. P. Vinogradov and I. I. Chernyaev success-
fully directed the creation of unique new methods of analysis, and a group under the direction of Academician
A. A. Bochvar and Corresponding Member of the Academy of Sciences of the USSR R. S. Ambartsumyan were
occupied with problems of metallic materials.
Many engineers, scientists, and technologists worked on the solution of these problems. On the part of
the Institute of Atomic Energy supervision of the graphite research was placed on N. F. Pravdyuk and V. V.
Goncharov.
Finally, it was necessary to coat the uranium with a weakly absorbing envelope.? it was necessary to
work out the material, the coating technology, and the technology for the control of these manufactured arti-
cles, as well as to develop a material, the technology for its preparation, and the technology for control of
pipes to organize cooling of the uranium in the reactor.
The second major direction was the separation of the isotopes of uranium. Here also several possibili-
ties occurred: the electromagnetic separation method, the diffusion method, the centrifuge method, the ther-
mal diffusion method, and various alternatives of them. All of these methods were exceedingly expensive and
cumbersome; however, research was organized in all these areas,
Finally, the third direction was the development of an intrinsically nuclear weapon ? the methods of
creating the needed large supercriticality. The possibilities of using systems with a moderator and the pos-
sibilities of systems based on fast neutrons without a moderator were investigated for this purpose. The
principles of the calculation of such systems had been created just before the war.
Scientists and engineers of the most diverse specialties were drawn on for the solution of these essential
problems. In addition to the specially created prominent scientific institutions in Moscow, Kharkov, and other
places, individual areas of the research were assigned to practically all physics, physical chemistry, and
chemistry institutes and to numerous institutes of industry. Industry was widely included in the research:
machine construction, chemical, nonferrous and ferrous metallurgical, aviation, and other branches of in-
dustry. The construction departments, which had been designing tanks, airplanes, and other forms of arma-
ment not long before,busiedthemselves with the new unprecedented work. The requirements put forward by
the scientists often seemed unattainable, but they were carried out all the same. The supervisors and parti-
cipants in all these efforts made an enormous invaluable contribution to the solution of the most difficult prob-
lem of mastering atomic energy [I was unable to cite in this section the family names of many scientists who
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played a large role in the solution of the problem, nor even the family names of the supervisors of important
activities. Therefore, I restricted myself in general to a very small number of family names in order to
avoid giving false impressions.]
The applied subjects enumerated above could not have been carried out on the proper level without basic
research in nuclear physics; investigation of nuclear cross sections, development of the theory of the nucleus,
investigation of numerous nuclear reactions, and numerous exploratory researches in areas bordering on the
atomic "problem." Solid-state physics, especially the behavior of matter at ultrahigh pressures and in ultra-
high magnetic fields, the behavior of matter under the action of radiation and other areas, metal physics,
radiochemistry, gasdynamics and explosion theory, mechanics, biology, genetics, and methods of analysis,
including mass spectrometry, were substantially developed in a short time. New kinds of equipment and new
materials were created in a short time; a cyclotron was constructed in a year altogether, and all of this took
place while the war, approaching the great victory, was still going on.
Finally came May 1945, and with it the greatest victory. Nazi Germany did not have time and was unable
to develop a nuclear superweapon. It would appear that the acuteness of the problem diminished.
But right after the victory information arrived about tests of an atomic bomb in the U.S.A. and about its
horrible destructive power. And right after this there followed the explosions at Hiroshima and Nagasaki,
which disposed of hundreds of thousands of lives among the civilian population at a time when victory in the
war with Japan was already predetermined without atomic explosions.
Why was this completely unjustified massive slaughter carried out? The purpose could only be the single
one of showing the world that the U .S.A . would not hesitate to use a nuclear weapon for the attainment of its
own political goals. These political goals were made clearer and clearer with each succeeding day. A monop-
oly in atomic power would, it seemed, give the U.S.A. enormous advantages and the American aggressive
circles began to develop ideas of a preventive war against the Soviet Union, and one could have expected any
military and political adventures.
Immediately after the capitulation of Japan the psychological preparation got underway in the United
States for a new war, a war against the Soviet Union. The speech of Churchill at Fulton and the start of the
organization of U.S.A . military bases around the Soviet Union were supplemented by the open discussion in
the press of the U.S.A. of how the atomic war against the Soviet Union should be organized. Diagrams were
presented in which the tracks of American nuclear bombers aimed at Moscow and other large cities were
shown by arrows, and the possible costs for an atomic attack, which, itwas suggested, should be organized prior
to when the Soviet Union solved the problem of producing an atomic bomb, were cynically estimated.
It became evident that it was necessary to destroy the monopoly on nuclear weapons before the United
States developed the production of such weapons on a scale which would represent a real threat to our country.
This realization was the main driving force for further development of the research. The Central Committee
of the Party and the Government continually and broadly supported research on the "atomic problem" and
rendered all the help needed.
Kurchatov and the great institute organized by him (now the I. V. Kurchatov Institute of Atomic Energy)
fulfilled the first of the tasks imposed on him and produced a uranium?graphite reactor.
In Dec. 1946 a chain reaction was accomplished by Kurchatov and his colleagues in the first reactor in
Europe, and in 1948 the first industrial uranium?graphite reactor was started up. The starting up of these
reactors and the production in the first of them of negligible microgram amounts of plutonium and in the second
of industrial amounts was the culmination of the enormous efforts of geologists, mining engineers, metallur-
gists and metallographers, chemists and radiochemists, nonferrous metal specialists, graphite specialists,
designers, and, of course, physicists ? experimentalists and theoreticians.
The organized work in the development of the uranium problem played an enormous role, and it was
successfully solved by a specially created government agency under the direction of B. L. Vannikov.
Kurchatov as the scientific director of the problem determined together with Vannikov and the other
supervisors the next tasks, and an undertaking of enormous size grew at rates previously unknown. The Amer-
icans assumed that the second way of solving the atomic problem, isotope separation, was generally unattain-
able for Soviet industry. However, an experimental factory was operating in the USSR already in 1947.
A likhanov, who had developed the approach of heavy-water reactors earlier at the Institute of Atomic Energy,
and then in a special institute created by him which has now received the name of Institute of Theoretical and
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Fig. 1. Beloyarskaya I. V. Kurchatov atomic electric power station.
Experimental Physics, also achieved success. The organizations drawn into the development of heavy water
set up this factory; a heavy-water experimental reactor successfully began to operate, and the first industrial
heavy-water reactor was created. The radiochemists successfully developed the technology of plutonium using
201.1,g of it produced by the manual uranium?graphite reactor. On the basis of their research, a plant for
the radiochemical extraction of plutonium from irradiated uranium was built which began producing plutonium
at the start of 1949. The majority of the physical measurements, further metallographic investigations, nu-
merous simulated explosion experiments which permitted finding the optimal means of producing supercriti-
cality, and finally the most detailed theoretical calculations which permitted finding the various principles of
producing nuclear charges preceded the first test.
And then we come to Aug. 29, 1949, when the successful test of an atomic bomb carried out under the
direction of Kurchatav (as the scientific director of the problem) shocked the whole world. The Americans
assumed that a nuclear weapon would not be produced in the USSR prior to 1954, and the supporters of a pre-
ventive war in the U.S.A. appealed for it to be unleashed before 1954, i.e., prior to the instant at which one
could expect the creation of a "Soviet atomic bomb."
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The creation of atomic bombs continuously increasing in power, the development of explosion theory,
and the detailed investigation of phenomena arising during an explosion made it possible to justify the idea of
a thermonuclear weapon. The theoreticians who suggested the idea of a thermonuclear bomb did not see any
fundamental limits to its power. The fusion bomb could be far more powerful than the fission bomb.
In order to create it, it was necessary to solve a number of complex technical problems; in particular,
it was necessary for some types of this weapon to develop methods for producing tritium and the light isotope
of lithium ? 6Li. The cumulative experience of solving large applied problems allowed carrying out these
processes on an industrial scale in a comparatively short time. The most complex research was concluded,
and on Aug. 12, 1953, a test of this monstrous superbomb was performed under the direction of Kurchatov..
Nuclear Power
Right now the development of nuclear power marks the next stage of growth in our country.
Already in 1948 ideas for the development of atomic power arose upon the solution of the uranium prob-
lem. Back then this idea encountered at best a smile. It was assumed that this was an "amusement" of the
scientists which would never be of practical significance.
Developments of channel uranium?graphite reactors for atomic electric power stations with water and
helium cooling, respectively, were being carried out at the Institute of Atomic Energy and at the Institute of
Physical Problems. The reactor with water cooling was selected for further development, and the first atomic
power station was designed by chief designer Academician N. A. Dollezhalt. It was constructed and put into
service in 1954 at the FEI in Obninsk. Although the power of the station was only 5000 kW in all, it proved
itself as a reliable source of electricity. A series of atomic power stations of continuously increasing power
was developed and constructed.
Right now many atomic power stations are constructed in our country and overseas based on our designs.
Of course, the use of atomic power not only for the production of electrical energy but also in other
areas of consumption of organic energy resources is important for the conservation of organic fuel. The
immediate areas are the production of heat for heating cities and the production of heat, electricity, and re-
generators for the metallurgical industry. Large-scale research is going in this direction.
Of course, all of this is meaningful only when one considers the inclusion in power generation of fast
breeder reactors with a short nuclear fuel breeding time. Only in this case can the nuclear fuel reserves
provide the needs of mankind for many centuries. The widespread development of atomic power brings with
it many complex problems, such as, e.g., the lengthy and dangerous storage of radioactive wastes. How-
ever, these problems are solvable, although difficult in the engineering sense. Atomic power is a very timely
gift of science to mankind and a supreme blessing, and it would be senseless to use this blessing for the de-
struction of mankind.
Along with the development of the atomic power of fission of heavy nuclei, research is going on now on
the atomic power of nuclear fusion and thermonuclear power having practically inexhaustible resources. This
is one of the most difficult scientific problems; however, it is being successfully developed. The mastering
of the energy of controlled thermonuclear fusion will fundamentally solve the problem of the long-term develop-
ment of human society on the earth.
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THE BIRTH OF NUCLEAR POWER
N. A. Dollezhal' UDC 621.039
Every beginning is difficult ? this truth holds for every science.
K. Marx
In our time, nuclear power has become an ordinary concept and there is no question about the need for
its development. In the USSR, as in many other countries, long-range plans are being elaborated for its de-
velopment, studies aimed at the improvement of the technical methods used are continually being made, and
both traditional and new basic and engineering? scientific disciplines are being developed. However, it is not
out of place to recall that the first nuclear power station in the world providing current to a commercial grid
was constructed in the Soviet Union and that I. V. Kurchatov was the initiator and director of its construction.
Under the direction of Kurchatov, the author of these lines was fortunate enough to be at the head of the major-
ity of engineering and structural developments from the very first days of nuclear technology. Since many of
them found application in subsequent accomplishments, these recollections, which are associated with them,
may be of interest.
My acquaintance with Kurchatov goes back to the end of 1945 and the beginning of 1946. At that time, I
was the head of the Scientific-Research Institute for Chemical Machinery Construction and apparently for that
reason Kurchatov decided to bring me in as the chief designer of a large reactor for achieving a self-sustaining
chain reaction through fission of uranium nuclei. There was no one with any experience in this field in the
USSR at that time, but probably he guessed that the field of chemical machinery construction was the closest.
Kurchatov said in jest that the only difference was that the reaction would proceed, so to speak, not on a molec-
ular level as occurs in chemical production, but on a nuclear level.
The first task in the development of a commercial nuclear reactor was set by I. V. Kurchatov in Jan-
uary, 1946. However, the very first studies showed that its realization was bound up with the need to over-
come very complex computational and technical difficulties. In Mar. 1946, the task was reviewed, a draft
plan approved, and the development of a technical plan was begun. By this time, many outstanding specialists
of our country were attracted to the solution of the completely new problem, and the outstanding talent of Kur-
chatov for interesting people in the work and for arousing their enthusiasm about its prospects played its part
in this.
The technical design for the reactor was reviewed by a commission of eminent specialists and construc-
tion was begun in Aug. 1946. Yet another quality of Kurchatov became apparent in this. You see, the start-up
of the zero-power experimental F-1 reactor had not yet been accomplished (it was started up only in Dec.
1946). Therefore, Kurchatov based his reliance on the correctness of the decisions made on a large number
of intermediate local studies intensively carried out under his direction through an extensive program in var-
ious institutes and in factories. To some extent, this can also explain the success which attended the start-up
of the experimental reactor RI.
It can be shown that such a means for solving a completely new problem, in both scientific and engineer-
ing aspects, has its risks. There is no doubt, however, that the main thing which Kurchatov did not question
was the need not "to delay," to solve the problem as quickly as possible. Later we all understood that it was
necessary to act in such a way because mankind was in an uneasy state at that time because of the tragic con-
sequences of the nuclear explosions above the Japanese cities of Hiroshima and Nagasaki. Concern was
aroused by the one-sidedness of the ownership of this type of weapon. It is noteworthy that such a method for
the solution of complex new problems became a part of practice and even now we do not see how it could have
been done otherwise.
The first commercial reactor, as is well known, was started up in 1948 [1]. It was for technical pur-
poses and no provisions were made for use of the heat created by the fission of uranium nuclei. However, the
means for realization of such a possibility under various circumstances were discussed throughout the period
Translated from.Atomnaya gnergiya, Vol. 44, No. 1, pp. 14-17, January, 1978.
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of reactor construction. Specific forms were accepted at the end of 1949 when ideas had matured about the
construction of an experimental device which would demonstrate the possibility of using heat from fission for
the production of electrical power. After preliminary discussions of a number of suggestions, the decision
was made to construct an experimental nuclear power station with an output of 5000 kW (electrical) in con-
junction with a turbine of that output which was available at that time. Of course, the steam parameters
which would be developed by means of the reactor were determined by the turbine characteristics.
Several basic requirements were formulated which had to be satisfied by the reactor; the possibility of
using for its construction knowledge already obtained about the performance of nuclear-physics reactor cal-
culations, and this meant that the reactor must operate with thermal neutrons; the neutron moderator had to
be graphite and the coolant ordinary water. Measures had to be taken to eliminate the consequences associated
with the entrance of uranium or its fission products into the coolant, which meant a tubular fuel element.
These and many other requirements were aimed at eliminating the possibility of producing any sort of trouble
during reactor operation, because that would inevitably compromise the idea of peaceful use of nuclear energy
and, it seemed to me, Kurchatov considered that unacceptable. This could explain the exceptional attention
he devoted to all the leading problems that arose during the construction of the reactor and nuclear power
station.
The events connected with the construction of the First Nuclear Power Station (and so it appears in in-
ternational listings) have been described in detail [2]. Its role as the first-born of nuclear power and that of
Kurchatov as father were universally recognized; its importance for future development of power reactors will
never be downgraded just as the importance of the work of Mozhaiskii in the development of aviation and the
outstanding work of Ts iolkovskii in rocket technology will never be forgotten.
The study of the possibilities of peaceful use of the heat from nuclear reactors was not limited to sta-
tionary power alone. Shortly after the decision was made to construct the Obninsk Nuclear Power Station, a
search was begun for possible ways to use this form of energy in ship construction. The vigorous measures
undertaken in this field by Kurchatov, as is well known, led to the construction in 1957 of the icebreaker Lenin
with a nuclear power plant by means of which extremely important problems for our country were solved that
had to do with prolongation of the period of Arctic navigation and with the possibility of piloting ships under
heavy ice conditions.
The First Nuclear Power Station was started up in 1954. But even before that, Kurchatov continually
raised the question of the need for development of more powerful plants. His faith in the future of nuclear
power was evidently so great that he unhesitatingly approved a suggestion to include draft studies of a nuclear
power station with a capacity of 100 MW in a report on the operation of the First Nuclear Power Station pre-
sented at the First Geneva Conference (1955) [3]. This produced a vigorous positive response from conference
participants. At this time, that number caused smiles, but at that time it was a daring challenge to those who
were inclined to be skeptical about the possible use of uranium for peaceful power. There were many of such a
mind even among very respected specialists.
As is well known, stainless steel was used in the tubular construction of the fuel elements in the First
Nuclear Power Station; this is a material that is not very favorable from the viewpoint of efficient use of neu-
trons, and therefore of uranium. A search was then undertaken which was directed toward the construction of
a power reactor using materials with favorable properties. A thorough analysis of possible solutions led to the
creation of the reactor which served as the basis for the construction of the Sibirsk Nuclear Power Station
with a capacity of 600 MW (electr ical). A film of such a reactor was shown to the participants at the Second
Geneva Conference in Aug. 1958 [4]. The reactor was designed and constructed in an exceptionally short time
and one cannot help but see the talents of Kurchatov in this. At the present time, science is enriched by know-
ledge in many fields such as the radiation resistance of structural materials, the behavior of uranium at var-
ious temperatures and in various nuclear-physics conditions, the production of corrosion effects, etc. At that
time, this knowledge was only being developed and decisions had to be made at times only on the basis of ini-
tial experimental data with the addition of scientifically valid foresight. However, it was necessary to act in
this way because there was no other way to gain the desired time.
The steam parameters developed by the reactors at the Sibirsk Nuclear Power Station were not high.
This was determined by the temperature allowed by the materials used. The undisputed tendency of power
engineers always was toward a possible increase in plant efficiency, which is particularly related to a rise
in the initial temperature of the coolant. It was necessary to find a reactor design which would make it pos-
sible to achieve the required superheating of the steam. After a large number of studies and experiments,
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such a solution was found ? reactors with nuclear (i.e., within the reactor) superheating of steam designed
in 1956 and constructed by 1963 for the Beloyarsk Nuclear Power Station that now bears the name of I. V.
Kurchatov. The reactors of this nuclear power station produce steam at a pressure of 90 kgf/cm2 and a tem-
perature of 510?C. In this sense, they are unique even in world technology [5].
Among the many problems which continually attracted the attention of Kurchatov were those involved
with the organization of methods which would make it possible to perform scientific and engineering studies
on a broad scale directed toward the development of nuclear engineering. Since the possibility of evaluating
results obtained in this way was usually directly dependent on the intensity of neutron fluxes with which the
experiments were performed, the construction of a research reactor with ahighneutron flux was necessary.
A design was produced in 1956 and by 1961 the special materials-testing SM-2 reactor was constructed in
which the neutron flux density in the test cells was 5 -10" neutrons/cm2.sec. This value was not exceeded
in any country during the course of the next few years. The boldness of the basic scheme and the original
structural solution for the reactor are cause for admiration even today. This reactor is faithfully serving
science even now [6].
Even while building the SM-2 reactor, Kurchatov had the idea of producing even higher neutron flux
densities, possibly in a pulsed mode. Thus, a reactor was created which was first called DOUD-3 and then
IGR. I remember Kurchatov called me in January, 1958 and asked me to come over to discuss an important
question. The question was the construction of a reactor which would consist of two graphite piles with the
required amount of uranium that, when brought together, would create criticality conditions for the occurrence
of a fission reaction, that would develop high neutron flux densities at required locations, and that would be
shut down by appropriate control methods in order to stay below permissible temperature limits. Several
structural hypotheses were discussed and the necessary engineering experiments performed; as a result of
all this, the reactor, despite its completely unusual structural arrangement, was approved for construction
(the reactor was started up in 1961). Important scientific and engineering problems are being solved with its
help at the present time [7].
However, Kurchatov did not consider all this sufficient. Possessing an outstanding capability for fore-
seeing technical development far into the future, before long (1958) he advanced the idea of constructing a
powerful materials-testing research reactor (MIR) with a large number of ports with high neutron fluxes for
experimental work [8]. The main thing that concerned Kurchatov was the need for testing fuel-element con-
struction before installation in a reactor. This can be done in a large number of special experimental loops
provided in the MlB structure (the reactor was started up in 1966). It must be recognized that it is quite
likely that for several years afterwards (indeed, even till today) everything related to the creation of nuclear
reactors owes a great deal to the farsightedness and correctness of the measures taken by Kurchatov in the
development of experimental work in nuclear engineering.
Unfortunately, Kurchatov did not get to see and actually become aware of the great fruitfulness of the
measures he took directed toward the development of nuclear science and technology in our country. We
learned to construct powerful reactors for nuclear power stations and we have available original types of
power reactors created completely out of his own independent and profound understanding of the physical,
engineering, and economic aspects of nuclear power. The foundations for this understanding were laid down
by Kurchatov and this was one of his historic services to his native land.
LITERATURE CITED
1. V. V. Goncharov, At. Energ., 42, No. 2, 83 (1977).
2. Twenty Years of Nuclear Power [in Russian], Atomizdat, Moscow (1974).
3. D. I. Blokhintsev and N. A. Nikolaev, in: Reactor Construction and Reactor Theory [in Russian],
Reports of Soviet Scientists at the First Geneva Conference, Izd. Akad. Nauk SSSR, Moscow (1955), p.
3.
4. Soviet Nuclear Science and Technology [in Russian], Atomizdat, Moscow (1967).
5. N. A. DollezhaP, At. Energ., 36, No. 6,432 (1974).
6. V. A. Tsykanov, At. Energ., 30, No. 2, 192 (1971).
7. I. V. Kurthatov et al., At. Energy., 17, No. 6, 463 (1964).
8. A. I. Bovin et al., USSR Paper 321, Third Geneva Conference (1964).
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THE PAST BECOMES HISTORY
L. M. Nemenov
Leningrad Physicotechnical Institute. The year was 1925. I. V. Kurchatov had just settled in at the
institute and was involved in the conductivity of dielectrics under the direction of Academician A . F. Ioffe.
K. D. SinePnikov was working with him. I was assigned to this laboratory as a laboratory assistant. Kur-
chatov's appearance made a strong impression on me. He was dressed very, simply. A velvet blouse, a
casually tied tie, dark trousers, and brown shoes worn at the heels. A tall, slender, dark-haired man who
carried himself well, he was very handsome. His eyes, dark and lustrous, were striking. He greeted me
affectionately, and asked what interested me and what I was able to do. All was simplicity and calm with him.
Shyness vanished at once. Kurchatov worked very intensely without thought for time. If he was not in the
laboratory, he was in the library. He had the distinctive hands of an experimenter. He did not avoid work of
any kind. Everything was done quickly but thoroughly. Everything was written down in a notebook. He said
there were no trivial details in our activities, everything was important, and the results must be written down
exactly. I worked with Kurchatov for only 2 months; A. F. Ioffe took me into his laboratory. I acquired my
oldest comrade and friend in the person of Kurchatov. Over the course of an entire lifetime our friendship
went unstrained by anything.
In 1935 Kurchatov proposed that I work together with him on a study of artificial radioactivity induced by
irradiation with neutrons.
He was already the head of a large section. As before, he worked day and night. However, his human
qualities remained unchanged. His treatment of all was even-handed and benevolent; he was not authoritarian
and he exhibited a great sense of tact. His ability to get away from extraneous matters was startling. When
working, he thought only of the problem he was solving at that moment. Our joint effort continued for about a
year.
In 1939 Kurchatov, having made arrangements with A. F. Ioffe, proposed that I transfer into his section
and participate in the construction of a large cyclotron with a pole diameter of 1200 mm. This cyclotron would
have been the largest in Europe. I accepted Kurchatov's proposal with pleasure and had the good fortune to
work under his leadership from that time until his death.
At that time, Kurchatov was also the head of a laboratory in the Radium Institute where the first cyclo-
tron in the Soviet Union with poles 1000 mm in diameter was put into operation under his direction and with his
direct participation. Kurchatov acquired considerable experience in the course of this activity.
The design and manufacture of individual elements of the cyclotron went ahead and a special building was
constructed. The outstanding organizational talent of Kurchatov was then revealed for the first time. The
construction of such a large cyclotron was an immense problem at that time. It must be pointed out that this
was extra work since the main efforts of Kurchatov were concentrated in the field of neutron physics. Start-
up of the accelerator was planned for Jan. 1942. However, the war upset all plans. Instead of going into
operation, the cyclotron had to be shut down.
At the beginning of the war, we were walking along the street with Kurchatov. A military unit was
approaching us. "You know, if I do not find real work needed by the country at this time, I will enter the
militia," said Kurchatov. How typical this was of him! He was a man of action and a true patriot. After a
few days, Kurchatov, having made arrangements with A. P. A leksandrov, joined in the work on degaussing
warships and served with the Black Sea Fleet in Sevastopol. A novel could be written about his activities
there.
In Feb. 1943 I was called to Moscow by official telegram at the request of Kurchatov. A. I. A likhanov
had received a similar telegram somewhat earlier. Having located A likhanov in Moscow, we went together to
Pyzhevsk where the seismic laboratory of the Academy of Sciences of the USSR was situated. There we found
Kurchatov and I. K. Kikoin.
Translated from Atomnaya E.nergiya, Vol. 44, No. 1, pp. 17-22, January, 1978.
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Fig. 1. Acceleration chamber of cyclotron.
We got down to business. Kurchatov reported briefly on a problem presented by the government. It
was a question of using subatomic energy for military purposes. I and my future group were charged with the
problem ? to produce the transuranic element 94 with the aid of a cyclotron in the shortest possible time. It
must be produced even if in trace amounts. A theoretical prediction was made of an important property of
this element, which is not encountered in nature (later, it was called plutonium). It was hypothesized that the
nucleus of element 94 could be split by neutron action just like the nucleus of 23 5U . This would mean the
appearance of a second material in which a fast chain reaction of the explosive type could occur. Micro-
amounts of plutonium were needed in order to carry out chemical studies on its separation in pure form.
It was proposed to produce element 94 in the following manner; the reaction
;Li + ;.d 113e + ;n
would be achieved by bombarding a lithium target with deuterons accelerated to 4-5 MeV in a cyclotron. The
neutron flux would be used to irradiate uranyl nitrate mixed with paraffin (the paraffin acted as a moderator).
It was proposed to produce element 94 by the following scheme:
2Np :;e-F2Pu.
In order to obtain a flux of deuterons with energies not less than 4 MeV, the pole diameter of the electromag-
net had to be 0.73 m and the magnetic field intensity 14 k0e. The wavelength of the high-frequency oscillator
had to be 28.3 m.
Sixteen months were allowed for the design, manufacture, and start-up of the cyclotron. The period
seemed incredibly short but it was approved by the government.
As already mentioned, a cyclotron was designed and partially constructed before the war at the Lenin-
grad Physicoteclmical Institute. Kurchatov proposed to speedily deliver to Moscow its high-frequency oscil-
lator, which was stored in Leningrad. There was no other way out; it was impossible to place an order for
so complex a device in Moscow at that time.
On the next day, we began to prepare for a flight to Leningrad. The trip to Leningrad was not easy.
Although our troops had broken through the blockade ring in one place in Jan. 1943, the fascists still sur-
rounded the city. We had to fly to Khvoina, wait there until darkness, and then make a low-level flight over
Lake Ladoga landing at Okhtinskii airport. In Leningrad, I tvas joined by engineer P. Ya. Glazunov.
The flight up was uneventful. The following day we set out for Smolnyi and delivered two letters. They
contained requests to the Leningrad managers to lend us all possible assistance. We had to report regularly
to Kurchatov on the way the assignment was being carried out.
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Kurchatov's assignment was fulfilled; all the equipment destined for dispatch to Moscow was loaded on
two freight cars and shipped on the railroad loop from Lesnyi to Tikhvin.
Before my departure from Moscow, Kurchatov asked me to visit his Leningrad flat and see what was
going on there. I quickly fulfilled his request. His flat was on Lesnyi Avenue in a building for specialists.
Going into the courtyard, I saw that an aerial bomb had demolished the outer wall of the house in which Kur-
chatov lived. It seemed as if one was looking at a fantastic stage setting. Reporting any information about
the destruction in Leningrad was not permitted; therefore, in a telephone conversation with Kurchatov, I
said that I was at his house but did not go upstairs since I saw the color of the wallpaper in his rooms from
the courtyard.
We reported to Kurchatov after our arrival in Moscow. He was pleased.
The group headed by Kurchatov was now called Laboratory No. 2 of the Academy of Sciences of the
USSR. Little by little, new workers began to arrive at Pyzhevsk, brought in a Kurchatov's request from var-
ious cities in the Soviet Union and recalled from the army.
Kurchatov went to inspect the future home of Laboratory No. 2. This was an unfinished building at the
All-Union Institute of Experimental Medicine in Pokrovsk-Streshnev. The place was bare and without vegeta-
tion of any kind. A dump was 50 m from the building. Railroad spurs were buried in mud. In time, new
buildings appeared, and a beautiful park, all of which is now called the I. V. Kurchatov Institute of Atomic
Energy.
While I was in Leningrad, Kurchatov drew up orders and placed them with Moscow factories for manu-
facture of the cyclotron electromagnet. Because of his energetic efforts, the forgings for the electromagnet
were ready at the end of May and were shipped to the Novo-Kramatorsk factory. Machining had to be accom-
plished to the required accuracy in the shortest possible time.
At the same time, design of the acceleration chamber was begun. All the small parts were handed over
to the experimental factory at the Institute of Combustible Minerals of the Academy of Sciences of the USSR,
and the large units to the Prozhektor factory.
Having arrived at the Prozhektor factory, we found out that there was a small shop at our disposal in
which there was a turret lathe. The chief engineer of the factory, having acquainted himself with the drawings
and tolerances for manufacture of the acceleration chamber, asserted that this was not in his line and that he
could not take on himself the responsibility for filling the order. He proposed that we ourselves work out the
technology and run the shop. Only 2 weeks were spent on the manufacture of the acceleration chamber.
Construction of a new building at Pokrovsk-Streshnev went ahead at a rapid rate. Removal was planned
for the beginning of 1944.
Kurchatov worked like one possessed. He slept little, but was always cheerful and friendly. No one
ever knew anything about his state of mind. Looking at him, one would think there were no difficulties what-
ever
At night, I used Kurchatov's desk as a bed. Kurchatov lingered over his work for a very long time, but
I had to get up at six in the morning in order to catch the train to Noginsk where the magnet was being manu-
factured. At one in the morning, I began to be concerned about when Kurchatov was going to quit. Somehow,
he could not contain himself and demanded "Do you want a job as my nurse?" But when he realized what was
occupying my "bed," he was a little embarrassed and from then on began to leave for home a little earlier.
We worked intensely at Pyzhevsk despite the crowded conditions. We helped one another any way we
could. A monolithic and friendly group was established. This was yet another service rendered by Kurcha-
tov. Typical of his style of leadership was complete confidence in those doing a job and the absence of petty
oversight. However, at the same time, he checked with great tact the quality of the work and the time taken
to fulfill a task. Extremely demanding of himself, he was able to impose the same demands on his associates,
and they regarded this as proper.
Subsequently, he succeeded in establishing large groups made up of people of high qualifications possess-
ing extremely individualistic characters. Such groups were united by a common purpose and by the indisputable
authority of Kurchatov. No one could deny that he was a charming person. He always asked that things be
done, but these requests were more forceful than any order. Because of his high principles, fairness, and
humanity, Kurchatov enjoyed the high esteem of all the groups with which he had to deal.
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Fig. 2. General view of cyclotron.
The day came for removal of the magnet from the factory. Early in the morning, the riggers, having
taken charge of the load, moved it along the route previously agreed upon by the militia. The magnet was set
up on a trailer and safely fastened with ropes. By noon it was in position, and 4 h later it was in place on its
base. Kurchatov dropped in several times to see how the magnet was being set up.
It was necessary to achieve a high vacuum in the acceleration chamber of the cyclotron and the system
had about 100 rubber gaskets. Now one had to consider under what difficult conditions one would have to per-
form assembly and adjustment of the accelerator. Every trifle was converted into a problem. leak detectors
did not exist at the time. We tightened the chamber by means of bolts and, with the lids clamped between two
cross-pieces, submerged it in a tank of water where a powerful electric lamp was installed for illumination.
Air from a compressor at a pressure of 3-4 atm was forced into the chamber. Looking for bubbles of air, we
determined the location of leaks, marked them, and then carefully sealed them.
Despite his tremendous work load, Kurchatov either dropped in on us or phoned, asking "if there was
any progress." He was in very much of a hurry, but we ourselves knew how important it was to get the job
done in the assigned time. You see, start-up of the cyclotron was the first "note" which Kurchatov had to
"meet" on the way to a solution of the entire gigantic problem.
After the elements of the accelerator were tested individually, assembly of the entire machine began.
Of course, not everything went smoothly. Small accidents occurred, but we pushed ahead with confidence.
Finally, assembly was completed and one could proceed to the acceleration of deuterons. On that day, Kur-
chatov left at eight in the evening for a conference with B. L. Vannikciv. However, knowing that a trial start-
up was being readied, he asked that we telephone him if "there was progress."
With a high vacuum in the acceleration chamber and the magnetic field on, it was necessary to apply a
high-frequency potential difference to the dees b For this, several hours of chamber "conditioning" were re-
quired in order to outgas its internal surface. After several hours, it began to hold the voltage.
We set the deuteron source into operation. We established the design wavelength of the high-frequency
oscillator and the intensity of the magnetic field. Small troubles showed up but we eliminated them rather
quickly. We adjusted the intensity of the magnetic field. Accelerated deuterons bombarded the target located
between the dees. It should have produced a neutron flux. The decisive moment had arrived. Everyone froze
in anticipation. A Geiger counter set up several meters from the cyclotron began to operate. There were
neutrons!
Everyone was worried if this were by chance. We increased the potential difference on the dees and the
number of clicks from the counter rose., Yes indeed, the deuterons circulating in the chamber traveled to its
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Fig. 3. Deuteron beam emerging from cyclotron.
periphery and struck the lithium target. Conditioning with the beam of accelerated deuterons was continued.
We began to measure the deuteron current directly with a measuring probe. We adjusted the intensity of the
magnetic field. We measured the maximum current. Fifty microamperes ! This was a triumph indeed!
Everything operated perfectly. We attempted to bring the beam out of the chamber. We installed a glass
plate with a fluorescing screen in place of the exit window. Once again we turned on the machine, applied a
negative potential to the deflection system, and varied the voltage ? the screen began to glow brightly. Stop!
We removed the glass plate and installed a previously prepared thin aluminum window.
This operation lasted for about 1 h. Everyone waited impatiently for the result. It took great effort to
perform the operation without undue haste. We turned on the magnetic field and the high-frequency oscillator,
and applied potential to the deflection system. Everybody held their breath. A deuteron beam emerged into
the air! It was quite visible. We turned out the lights and the bluish-violet plume at the window of the accel-
eration chamber showed even more clearly in the darkness. We shut down the cyclotron.
I telephoned B. L. Vannikov. He himself picked up the receiver. I greeted him and asked to talk to
Kurchatov. "Well, did the cyclotron work?" asked Vannikov. "No, it's simply that Kurchatov asked me to
call." Kurchatov came to the phone and immediately asked, "Did it work?" What was the current? "Something
over 50 ?A A. We extracted the beam and saw it by its own light," I replied. "Turn it off so that nothing goes
bad. Expect me in 1 h. I congratulate you and give my congratulations to the boys."
It was two in the morning. In the laboratory notebook was written "On Sept. 25, 1944, a deuteron beam
was extracted from a cyclotron for the first time In the Soviet Union and Europe."
As promised, Kurchatov arrived in 1 h, cheerful, laughing, and excited. "Nothing happened?" was his
first question.
We turned on the machine and the long-awaited beam appeared once again. Kurchatov was satisfied and
asked us to measure the internal current with the probe. It turned out that the chamber had become condi-
tioned and the current increased to nearly 100 ?A . Then Kurchatov asked for neutron irradiation of a silver
foil in a lump of paraffin. We brought the irradiated foil toward the Geiger counter; the counter "jammed"
when we were 2 m away.
It was already four in the morning. Kurchatov congratulated us once more and invited us to his house.
He was so pleased and happy that it was impossible to refuse him. We went there and woke up his wife. She
was frightened but laughed when she found out what this was all about. Kurchatov brought out a bottle of cham-
pagne and we split it. Taking leave of us, he said, "Tomorrow we shall make additional measurements with
paraffin blocks and the day after tomorrow we shall begin the irradiation of uranyl nitrate."
Thus ended a remarkable working day for us that almost lasted 24 h.
Kurchatov divided the entire staff into brigades for performing the experiments on the development of
irradiation techniques. He headed one of the brigades himself. The experiments went on around the clock.
Then the irradiation of uranyl nitrate began. It continued until Dec. 1945. The irradiated material was sent
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for separation of plutonium to the laboratory of the chemist Boris Vas il'evich Kurchatov, the brother of Igor
Vasirevich.
B. V. Kurchatov and his associates developed the so-called sulfate method (coprecipitation from an
aqueous solution) for separation of the plutonium produced as the result of uranyl nitrate irradiation in the
cyclotron.
This method was worked out with the first microamounts of plutonium first produced in the Soviet Union
by B. V. Kurchatov in Oct. 1944 from 1.5 kg of uranium irradiated with neutrons from a Ra ?Be source. The
first cyclotron plutonium in Europe was separated by this same method. Thus, the problem formulated by I.
V. Kurchatov in March 1943 was solved.
The war was coming to a victorious conclusion. However, the pace of the work at Laboratory No. 2 did
not slacken. The number of staff members increased considerably. Kurchatov had new concerns.
No scientist in the Soviet Union had to direct such large groups before this and no scientist enjoyed such
confidence from the party and government as I. V. Kurchatov. In this man, nature combined the talents of an
outstanding scientist with the talents of a remarkable organizer.
SPONTANEOUS FISSION OF HEAVY NUCLEI
K. A. Petrzhak and G. N. Flerov UDC 539.173.7
Since the discovery of the spontaneous fission of uranium ? work done under the scientific guidance of
I. V. Kurchatov ? almost 40 years have passed. During these years spontaneous fission has become an im-
portant branch of the physics of the atomic nucleus. Today, interest in spontaneous fission is due, on the one
hand, to the fact that it is the simplest example of a large-scale nuclear phenomenon connected with the mo-
tion of a large amount of nuclear material. On the other hand, it is a fundamental process determining the
stability of heavy nuclei, so that the question of spontaneous fission is closely related to the problem of the
boundaries of D. I. Mendeleev's periodic system of the elements, and hence to some problems of chemistry,
geophysics, and astrophysics..
Paying tribute to the memory of our teacher, we give below a summary of some fundamental results and
endeavor to outline future prospects in the study of spontaneous fission, a new form of radioactive disintegra-
tion of heavy elements.
Brief Historical Outline
In 1934 E. Fermi and his co-workers, attempting to obtain transuranium elements by bombarding ura-
nium with slow neutrons, discovered a considerable number of activities which they attributed to various iso-
topes of radium and hypothetical transuranium elements. This was the beginning of a kind of "gold fever" in
nuclear physics, which led in 1939 to the discovery of nuclear fission [1,2].
The classical works of Frenkel' [3], Bohr and Wheeler [4] developed the first theory of fission, based
on the liquid-drop model. Bohr and Wheeler also indicated the possibility of spontaneous fission, but they
estimated that the lifetime of uranium nuclei with respect to this process had the astronomically high value of
1022 years. Also in 1939, Libby of the University of California made an attempt to discover the process of
spontaneous fission of uranium and thorium nuclei [5]. The first series of his experiments concluded with the
search for radioactive fragments in a natural mixture of isotopes, the second with an attempt to detect secon-
dary neutrons formed during fission. Both series of experiments led to negative results, and the lower bound
of the lifetime of uranium and thorium with respect to spontaneous fission was estimated at 1014 years.
At that time, nuclear-physics research was only beginning to develop in our country. The teams of
young scientists headed by I. V. Kurchatov at the Physics and Technology Institute and the Radium Institute in
Leningrad were confronted with a complex problem: to make Soviet research catch up in as short a time as
possible and to bring their work out into the "world arena."
Translated from Atomnaya inergiya, Vol. 44, No. 1, pp. 22-36, January, 1978.
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Thanks to his profound scientific intuition, I. V. Kurchatov was able to appreciate the importance of the
fission process as soon as it was discovered, and he concentrated the energies of the teams under his guid-
ance on the study of fission. This was a demonstration of one of I. V. Kurchatov's fundamental characteris-
tics ? the ability to select an important line of investigation and to formulate problems whose solution would
determine the fate of the problem as a whole. It was possible to make qualitative progress along this path by
the development of experimental methods whose sensitivity would be considerably higher than that of the meth-
ods existing abroad at that time.
To us, who were still very young investigators at that time, I. V. Kurchatov assigned the problem of
determining with high accuracy the threshold of natural fission of a natural mixture of uranium isotopes. It
was decided to record the fission fragments by means of an ionization chamber with a sensitivity much higher
than those used previously. As a result of many experiments, we set up a multilayer chamber with a working
area of the plates equal to about 1000 cm2, on which we were able to place about 30-50 times as much uranium
as usual. Later we designed a chamber 200 times as sensitive as the usual kind. In the course of the work
we had to overcome a great many technical difficulties connected with the design of a special amplifier tuned
to the fragment pulses, the problems produced by noise, the microphone effect, etc. Overcoming these dif-
ficulties meant essentially that we had to work at a level considerably higher than that of the technology pre-
vailing at the time.
In the first experiments we observed spontaneous pulses in the absence of a neutron source. The number
of pulses was small ? about 6 per hour ? and it was therefore quite understandable that they had not been dis-
covered earlier, with chambers of the usual type. When we informed I. V. Kurchatov of these remarkable
results, he said that if this was really spontaneous fission, we would have to throw everything else aside and
spend all our time on this ! There followed a great many discussions, as a result of which the necessary con-
trol experiments were designed and carried out. They successively eliminated the possibilities that the
"spontaneous" pulses were caused by radio noise, the repeated application of pulses from a particles, etc. A
comparison of the amplitude distributions of the "spontaneous" pulses and pulses from induced-fission frag-
ments showed that they were identical and convinced us still more firmly that we were indeed observing spon-
taneous-fission fragments.
Although preliminary estimates had indicated that the fission of uranium by cosmic rays made only an
extremely small contribution to the observed effect, we had to verify this experimentally. Here we saw a
demonstration of another characteristic of I. V. Kurchatov's ? the ability to change the course of an investi-
gation quickly, bringing it into new conditions: on his recommendation, we began to conduct our further in-
vestigations in a shaft of the Moscow subway, at a depth of 50 m. In the first place, at that depth the intensity
of cosmic rays is reduced by a factor of about 40, and in the second place, the new conditions themselves ex-
cluded to a considerable extent the influence of unforeseen factors acting at the surface of the earth, partic-
ularly at an industrial and technological center such as Leningrad. As the series of experiments conducted
lathe Moscow subway showed, the spontaneous-fission effect underground was the same as on the surface.
This gave the answer to the critics (quite numerous at that time) who asserted that the effect was entirely due
to the action of cosmic rays. It must be stated that a large part of the difficulty consisted in the fact that very
little was known at that time even about induced fission. Naturally, this inevitably led to a considerable in-
crease in the number of control experiments we had to conduct. As a result of this intensive and lengthy pro-
gram of work, we concluded that "the effect we have observed should be attributed to fragments obtained as a
result of the spontaneous fission of uranium" [6].
The success of the experiments conducted in Leningrad was due primarily to the qualitative improvement
lathe sensitivity of the methods used, making it possible to detect events which occurred very seldom. In the
course of this work we acquired a store of experience in the recording of infrequent events which was often ex-
tremely helpful in our later investigations.
Although I. V. Kurchatov was the scientific leader of the entire cycle of investigations, he scrupulously
refused to become a co-author of the publications on spontaneous fission. Commenting on his invaluable con-
tribution, we wrote in the first article: "... We wish to express our sincere gratitude for the guidance of the
work by Professor I. V. Kurchatov, who planned all the control experiments and took a very direct part in the
discussion of the results of our investigations" [6].
In 1943 Pose [7], recording neutrons accompanying the spontaneous fission of uranium, confirmed our
results. In 1944 M. I. Pevzner and G. N. Flerov, having considerably improved the sensitivity of the method,
radiochemically isolated some radioactive isotopes of iodine. This proved the presence of spontaneous-fission
fragments in a natural mixture of isotopes, i.e., achieved what Libby had been unable to do earlier.
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The war interrupted our investigations on spontaneous fission, forcing us to devote our primary atten-
tion to questions which were of enormous importance to the state. The outstanding role played by I. V. Kur-
chatov in the successful solution of the problems that arose in that connection is well known.
The renewal of basic research in nuclear physics in the 1950s made it possible to continue the study of
spontaneous fission along two main lines which developed in close interaction with each other.
The first line of research was related to the detailed investigation of the mechanism of spontaneous fis-
sion and included not only the determination of the probability of spontaneous fission for various transuranium
elements but also the study of the characteristics of the process that were related to each individual spon-
taneously fissionable nucleus [8-10].
The 1960s brought a qualitatively new stage in the study of the mechanism of spontaneous fission: the
Soviet atomic industry, whose establishment and development is inseparably connected with the name of I. V.
Kurchatov, began to make appreciable quantities of artificial transuranium elements available to researchers.
It became possible to measure in detail the characteristics of the process ? the energy distributions of the
fragments, the yields of fragments of different masses which helped to explain the effect of quantum effects on
the fission process, neutrons and y quanta accompanying the fission, etc. [11-13]. It gradually became clear
that for the study of such a complex phenomenon it is not enough to measure any single parameter character-
izing the fission process for a particular nucleus. Further progress in the study of such a problem as, e.g.,
the dynamics of the fission process, is the result of multiparameter investigations which were begun during the
late 1960s, involving the simultaneous measuring of three, four, and even five fission characteristics [14-16].
A special place in the investigation of the mechanism of spontaneous fission is occupied by the study of
the fission that accompanies the emission of light charged particles ? protons, tritons, a particles, etc. [17-
19]. Since the emission of light particles takes place at an instant close to the separation of the fragments,
the investigation of this process could and did provide valuable information on the properties of a fissioning
system. Fission with the emission of a third light particle is a process with very low probability (e.g., for
500 cases of binary fission there is one emission of an a particle, and the probability of the emission of other
particles is even lower), and therefore in order to study it, it was necessary to devise complicated experi-
mental methods designed for the recording of very infrequent occurrences. In the investigation of the com-
position of light particles it was unexpectedly found that during the process of ternary fission there are emitted
light nuclei with a large excess of neutrons (e.g., helium isotopes from 5He to te), the investigation of whose
structure is a matter of interest in itself [20, 21].
The investigation of some characteristics of spontaneous fission is also of considerable applied signifi-
cance. This involves primarily the exact determination of the number of neutrons per spontaneous fission of
252Cf, a very important reference parameter for many relative measurements whose results are directly
utilized for the calculation and forecasting of fast reactors, the measurement of spectra of prompt fission
neutrons of transuranium elements, the cross sections of fission of heavy nuclei by neutrons from the spon-
taneous fission of 2 52C f, etc. [22-24].
The second line of research on spontaneous fission was connected with the explanation of its role as one
of the decisive factors in the problem of the stability of heavy nuclei, and consequently in the question of the
boundary of the periodic system of the elements. At the beginning of these investigations, eight transuranium
elements were already known, including fermium (Z =100), obtained by multiple capture of neutrons in high-
density neutron fluxes.
Qualitative progress on the path of artificial synthesis of even more remote transuranium elements could
be made only by utilizing nuclear reactions caused by heavy ions.
Such reactions would make possible a "jump" increase of several units in the atomic number of the syn-
thesized elements. The problem consisted in proving the theoretical possibility of accelerating ions whose
mass was 10-20 times the mass of a proton.
With the ideological guidance and strong support of I. V. Kurchatov, in 1954 the first experiments on
the acceleration of nitrogen ions were begun on the 150-cm cyclotron of the Institute of Atomic Energy in
Moscow, and by the end of the 1950s, as a result of the creation of a powerful source of mufticharge ions that
was capable of providing a monoenergetic beam of nuclei of carbon, nitrogen, and oxygen with the necessary
energy, researchers were able to complete the first cycle of investigations designed to explain the main fea-
tures of the interaction of multicharge ions with nuclei [25,26]. The very first studies of the cycle showed the
exceptionally promising nature of the use of heavy ions for the artificial synthesis of new transfermium ele-
ments, and in 1956 experiments aimed at obtaining the previously unknown element 102 were begun.
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The successfully developing new line of investigation in nuclear physics continued to receive the consis-
tent attention and strong support of Academician I. V. Kurchatov, on whose recommendation it was decided
that the investigations with heavy ions should be considerably expanded. In 1957, at the Joint Institute for
Nuclear Research (JINR) at Dubna, the Nuclear Reactions Laboratory was established, on the basis of a new
accelerator designed especially for accelerating heavy ions.
A classical cyclotron with poles measuring 310 cm in diameter was designed; it became operational in
1960. It remains one of the leading installations in the world to this day in intensity and in the variety of
accelerated particles. As a result, it became possible to pass to systematic basic research aimed at the
synthesis of new transfermium elements lying on the boundary of the region of nuclear stability.
On the basis of many methodological developments and investigations of the mechanism of nuclear reac-
tions between complex nuclei, in 1964-1970 new transfermium elements with atomic numbers 102, 103, 104,
and 105 were synthesized, and their physical and chemical properties were studied [27,28]. In recognition of
the outstanding scientific services rendered by Academician I. V. Kurchatov, element 104, discovered by
Soviet scientists in 1964, was given the name of "kurchatovium."
Detection of the a disintegration of nuclei was preferentially used for identifying elements 102 and 103.
For elements 104 and 105, another approach to identification, based on the recording of their spontaneous fis-
sion, was developed and applied. The reasons for this were the following. In the first place, while spontaneous
fission is a rather infrequent form of disintegration for nuclei with Z 105 by the traditional method ? the irradiation of
targets made of heavy transuranium elements (Cm, Cf) with relatively light ions (0, Ne) ? was considerably
complicated by the fact that when we use targets which themselves have a high fragment activity, there is a
sharp increase in the probability of the formation of spontaneously fissionable isotopes of fermium as a result
of nucleon-transfer reactions. Both of these factors lead to the formation of a high fragment background.
Furthermore, the compound nuclei obtained in such combinations have an excitation energy of -40-50 MeV,
and the successive emission of neutrons can reduce only 10-2-10-10 of them to the ground state. As a result,
the formation of each successive new element by this method becomes a more and more infrequent process.
Continuing along the path of accelerating heavier and heavier particles and utilizing nonradioactive tar-
gets, the workers of the Nuclear Reactions Laboratory developed a method for synthesizing transfermium ele-
ments which was based on the formation of weakly excited compound nuclei during the bombarding of targets
made of lead with accelerated ions of argon, titanium, chromium, etc. [29]. This method is free from many
difficulties that arise in the traditional approach to the synthesis of new elements, and the absence of a back-
ground makes it a highly sensitive method for the detection of spontaneous fission. The use of this method did
in fact lead to the discovery of the elements with atomic numbers 106 and 107 [30,31],
Further prospects are connected with the utilization of accelerated ions of the "Ca type, which offer
exceptional possibilities for the artificial synthesis of elements [32]. The structure of this nucleus is such
that above the filled doubly magic core of "Ca there are eight neutrons. Its restructuring upon coalescence
with another nucleus requires a large expenditure of energy, which means that the resulting compound system
has a low excitation energy, and the "excess" neutrons prove to be very important in making advances toward
the region of large values of Z and N. Despite many difficulties, by today we have obtained fairly high-intensity
beams (more than 1012 particles per second) of these very exotic nuclei, and work has been begun on the syn-
thesis of elements 108 and 109.
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36 38 40 42 44 Z2 /A
Fig. 1. Relation between the half-life periods of
heavy nuclei with respect to spontaneous fission,
Tsf, and the fissionability parameter Z2/A : 0) even
?even nuclei; A, 12) odd nuclei.
We will not dwell at this point on other lines of development of heavy-ion physics, such as the artificial
synthesis of light and intermediate nuclei far from the region of fl stability [33], the study of deep-inelastic
transfer reactions [34], delayed protons [35], the synthesis and investigation of new isotopes of rare-earth
elements [36], the problems of atomic physics and electrodynamics involved in the collision of heavy ions [37],
etc. Present-day achievements and prospects of development in this promising direction of nuclear physics
are enormous [38]: by the early 1970s, researchers had formed the opinion that the nuclear physics of the
coming decade or two will be primarily the physics of heavy ions We cannot fail to note, of course, that the
use of heavy ions also offers unique opportunities for the solution of many applied problems of today [39].
Some Important Achievements in the Study of
Spontaneous Fission
During the 38 years that have passed since the discovery of spontaneous fission, more than 100 isotopes
In the transuranium region have been synthesized. About 50 nuclei out of the 100 undergo spontaneous fission.
For most of these nuclei the half-life periods for spontaneous fission have been determined fairly accurately;
for some, only the lower bounds of the periods have been obtained. For many nuclei in this region the values
of the fission barriers have also been experimentally determined.
The first attempts to systematize the spontaneous-fission periods, which made it possible to clarify the
overall picture of the stability of heavy nuclei with respect to this form of disintegration, date from the early
1950s'[40,41]. It was established at that time that the periods of spontaneous fission of even-even nuclei de-
crease according to an approximately exponential law as the fissionability parameter Z2/A increases. This
agreed qualitatively with the predictions made on the basis of the classical drop model, according to which the
probability of spontaneous fission can be directly determined from the parameter Z2/A , a measure of the ratio
of repulsive Coulomb forces to the surface-tension forces that stabilize the nucleus. For a critical value of
the parameter, (Z2/A)cr 48, the fission barrier completely disappears, and then the lifetime of the nucleus
with respect to spontaneous fission is -10-22 sec. It would appear that we obtain a rather simple picture: the
periods Tsf of spontaneous fission of all the transuranium elements lie in an interval between -1016 years, the
spontaneous-fission period for 23kJ as measured in 1940, and -10-22 sec, corresponding to the lifetime of an
absolutely unstable nuclear system. All other points lie on an exponential curve drawn between the extreme
values, so that the 1940 measurement yields, in a certain sense, a large-scale calibration of the stability of
nuclei with respect to spontaneous fission.
However, the appearance of new data concerning spontaneous-fission periods of transuranium elements,
and later those of transfermium elements, made it necessary to correct the simple liquid-drop picture. From
the relation shown in Fig. 1 it follows that there are substantial effects that cannot be explained within the
limits of the classical model. In the first place, there is the large (103-106) forbiddenness parameter for iso-
topes with an odd number of nucleons. Thus, for 238pu. the value of Tsf is 4.9 .10" yr, whereas for 239Pu it is
5.5 .10" yr, for 256Fm it is 2.7 h (2 .10-4 yr), and for 2571'm it is 102 yr; the addition of one nucleon to an even
?even core leads to a sharp increase in the stability of the system. In the second place, in the liquid-drop
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105
100
105
Z-98
ma 100 AL
Illir 102 Mill
I WINIIIME
NIIM
AIME&
iwairm
?sta
y !_;, ;
mc .104 1??I !
/
MKC /
/ \
/
144
148
152
156
Fig. 2. Half-life periods for spontaneous fission, Tsf,
as functions of the number of neutrons N for the heaviest
even?even nuclei; 0.) even ?even nuclei; 0) odd
nuclei.
model the fission barrier, and consequently Tsf for isotopes of a single element, must increase monotonically
as A increases, i.e., as Z2/A decreases. However, in the curves connecting the values of the spontaneous-
fission periods of different isotopes of a single element we usually find maxima.
As the number of protons in the nucleus increases, the half-life periods of isotopes of a given element
become more strongly dependent on the number of neutrons N; e.g., for isotopes of fermium or of element
102, a change of two units in the number of neutrons leads to a decrease in stability with respect to spontan-
eous fission by a factor of 104, as can be seen from Fig. 2.
At the same time, the nature of the variation of the stability of even?even isotopes of kurclvdovium as
a function of the number of neutrons is radically different from the analogous functions for californium, fer-
mium, and element 102. As was shown by Oganesyan et al. [42], the variation of Tsf for isotopes of kurcha-
tovium indicates a monotonic increase in the lifetime of even?even nuclei of Ku with increasing mass without
any substantial variation in the region N = 152, whereas for other nuclei there is a great deal of variation.
From all of these facts we can draw the physical conclusion that the drop model represents only a crude
average picture and that the internal structure of the nucleus plays a very important role in the fission process.
Many attempts have been made to take account theoretically of the effect produced on the probability of
spontaneous fission by the structure of the nucleus, but for a long time they remained unsuccessful. Without
discussing all these investigations in detail, we should recall the work of Myers and Swiatecki [43], who attemp-
ted to combine the liquid-drop model with the independent-particle model. They assumed that the shell correc-
tion to the liquid-drop mass of the nucleus, related to the reduced or increased density of single-particle levels
near the Fermi boundary, is maximal for near-magic and spherical nuclei and decreases exponentially as the
deformation increases. On the basis of such assumptions, they calculated the equilibrium deformations of the
nuclei and also the height and shape of the fission barriers. Myers and Swiatecki extrapolated their calculations
to the region of superheavy nuclei, and, as it turned out, near the assumed magic numbers Z = 126, N =184,
taking account of the shell correction leads to the appearance of a barrier -9 MeV high, i.e., to the possibility
that superheavy nuclei which have a high stability with respect to spontaneous fission may exist in this region.
The Myers ?Swiatecki model was proved wrong by a systematic study of the fission thresholds of heavy
nuclei (Z2/A = 34-38) which are deformed in the ground state. The experiments showed that in this region of
nuclei the fission thresholds remain almost constant, whereas according to the calculations they should
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decrease by a factor of several units. The fact that these fission thresholds were constant contradicted Myers
and Swiatecki's fundamental assumption that the shell correction has a stabilizing effect only in the region of
spherical near-magic nuclei and disappears in the region of deformed nuclei. The divergence between theory
and experiment was impossible to explain even qualitatively.
Equally unsuccessful were the many attempts at purely microscopic calculations to describe strongly
deformed nuclei in the fission process on the basis of a scheme of single-particle levels in the deformed
Nilsson potential [44,45]. The use of this method proved to be possible-only for small deformations. The
fission barrier in calculations of this type was obtained as a small difference between two energies with large
absolute values - the surface energy and the Coulomb energy - and the schemes of levels were not well
enough known to calculate the surface energy accurately.
The situation changed considerably when in 1962, in Dubna, during experiments on the synthesis of a
new element with atomic number 104, it was found that the nucleus of 242AM undergoes spontaneous fission
with a half-life period of about 0.014 sec [46]. This period was impossible to attribute either to induced fis-
sion (the lifetime of such a system is less than 10-16 sec) nor to spontaneous fission from the ground state
(Tsf - 1014 yr).
The investigations conducted in Dubna and at other leading laboratories throughout the world showed that
the existence of two half-life periods of this nucleus with respect to spontaneous fission was by no means a
unique phenomenon.
Today more than 30 such nuclei have been identified in the region from uranium to berkelium with "anom-
a1ousw half-life periods of 10-9-10-2 sec, obtained both in reactions with heavy ions and upon the irradiation
of heavy nuclei with neutrons of different energies, down to thermal neutrons, gamma quanta, and light charged
particles [47].
Bohr and Flerov [48] proposed interpreting this very interesting phenomenon as fission from an isomeric
state whose deformation considerably exceeds the equilibrium deformation, i.e., as an isomerism of shape.
The discovery of fission from the isomeric state stimulated the development of a new theoretical
approach [49,50] both to the problem of stability of heavy nuclei and to the shell model as a whole, which in
turn made it possible to give more concrete content to the hypothesis of isomerism of shape. This was done
by V. M. Strutinskii.
In the original variant of his theory the quantum correction to the total nucleus energy was due to the
nonuniformity of the single-particle spectrum in the region of the Fermi boundary. However, as V. M.
Strutinskii showed, the correction does not disappear when the shape of the nucleus differs from the spherical
- the quantum nonuniformities near the Fermi boundary may be preserved up to very high deformation values,
stabilizing the system. Therefore, the phenomenon of "magicness" may occur even in severely deformed
nuclei. In particular, during the fission process there is a periodic redistribution of the nonuniformities of
the levels, leading to increased stability of some shapes of the fissionable nucleus. The potential energy of
the nucleus, for certain deformations, has minima corresponding to filled "large shells" - regions of increased
density of the single-particle levels.
For nuclei undergoing isomeric fission, there are two such minima (and corresponding maxima). The
first minimum corresponds to the ground state of the nucleus, and the second to the isomeric state. If in the
fission process the nucleus falls into the second well and its energy is less than the height of the barriers sur-
rounding the well, it is captured. It is possible in this process to have either fission from the second well,
the probability of which is determined by the shape of the second barrier, or radiative transition from the
isomeric state to the ground state through a tunnel transition under the first barrier. This theory offers a
possibility of correctly calculating the energy of the nucleus for large deformations, and consequently the
shape and height of the fission barriers.
Many calculations carried out by Strutinskii's method showed [51-53] the existence of a rather broad
region of nuclei in the region of the doubly magic nucleus 298114, where the height of the fission barriers
reaches 10 MeV.
However, it should be stipulated that the errors due to the extrapolation of the parameters of the single-
particle potential in the region of superheavy nuclei may be very large, and this affects the accuracy of the
calculation of the potential energy of the nucleus as a function of its deformation, in particular the height and
shape of the fission barrier.
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This applies even more to the calculation of the periods of spontaneous fission of heavy and superheavy
nuclei, which is an extremely complicated problem. The potential energy of the nucleus, calculated as a func-
tion of its shape, is not yet enough to determine the dynamics of the motion of the fissioning system up to the
point of separation. A knowledge of the potential energy makes it possible to calculate the forces acting in
the nucleus; however, the further solution of the complete dynamic problem requires a determination of such
properties of the fissioning nucleus as its inertia or the related dissipation of collective energy on the basis of
other degrees of freedom. Thus, e.g., it becomes necessary to introduce effective coefficients of inertia
which have been subject to the influence of the shell structure of the nucleus to no less a degree than the pote.
tial energy itself.
At the same time, the calculations of effective coefficients of inertia is a problem which is less clearly
defined in principle than the calculation of the potential energy, since its solution requires the introduction of
additional assumptions which are not always justified.
Up to the present time, theoretical calculations [54-56] have been carried out for the spontaneous-
fiss ion half-life periods of the heaviest nuclei, and on the whole, they have reproduced the experimental data
reasonably well ? the functional relations with "maxima" for fermium and element 102, the considerable var-
iation in the systematization when we go from Z =102 to kurcbatovium, the even? odd effects, etc. Although
these attempts are of considerable importance for the further development of the theory of fission, their sen-
sitivity to details of the calculation is such that each of the indeterminacies ? 1 MeV in the height, 5% in the
width of the barrier, or 10% in the mass parameter ? leads to a variation in Tsf by a factor of about 100 [57].
Therefore, it is still impossible to expect an accuracy in the calculation of the periods of spontaneous
fission of heavy nuclei, and especially of superheavy nuclei, better than 10?8 yr.
Superheavy Nuclei
For the physics of the atomic nucleus, one of the most important consequences of the experimental and
theoretical investigations of the spontaneous-fission process is the prediction of a possible region of super-
heavy elements. The sum total of our knowledge of the atomic nucleus and its quantum stability, obtained
over the past four decades, makes this prediction fairly reliable and independent, in general, of the choice
of any particular variant of the shell model. An answer to the question of the existence of superheavy elements,
obtained experimentally, would perhaps signify the most critical verification of the very concept of the shell
tructure of the nucleus, the fundamental nuclear model, which has stood the test of time very successfully
but nevertheless is still a model.
More concretely, the stability of heavy nuclei is determined chiefly by their spontaneous fission, and
therefore a necessary condition for the existence of such nuclei is that they have a barrier with respect to
fission. For nuclei from uranium to fermium the shell component of the fission barrier, leading to some very
interesting physical phenomena, nevertheless does not have a critical effect on their stability, appearing in
superposition with the liquid-drop component of the barrier. In the region of superheavy elements the drop
component of the barrier completely disappears, and the stability of superheavy nuclei is determined by the
penetrability of a purely shell-type barrier. Thus, the existence or nonexistence of superheavy elements is
directly related to the question of whether or not the fundamental ideas concerning the structure of the nucleus,
based on the shell model, are valid. On the other hand, while the presence of a barrier is sufficient for the
theoretical existence of superheavy nuclei, for experimental verification of such a prediction we must have a
knowledge of the lifetime of the superheavy nuclei with respect to spontaneous fission, since for any concrete
formulation of the search experiment it is impossible to include the entire lifetime range from 1010 yrto 10-19
sec. The choice of the principle of the experiment is determined essentially by the lifetime interval in which
the investigation is conducted.
As has already been said, the indeterminacy of the theoretical calculation is too great ? 8-10 orders of
magnitude. This indeterminacy does not a priori exclude any of the possibilities of obtaining or discovering
superheavy elements, and for a line of experimental investigation to solve the problem we may choose either
a search for superheavy nuclei in nature (on earth, in objects of cosmic origin, in the composition of cosmic
rays, etc.) or the artificial production of elements in accelerators (in nuclear reaction between complex
nuclei).
We would like to make some remarks concerning the search for superheavy nuclei in nature. It is
obvious that the search for superheavy elements in terrestrial objects can bring success only if the lifetime
of these elements is comparable to the lifetime of the earth, which is 4.5 yr. Such investigations have
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been conducted on an extensive scale during the past decade, and we can say even today that a number of ob-
jects that are very promising in this respect have already been determined.
Equally promising is the search for superheavy elements in objects of extraterrestrial origin ? meteor-
ites, cosmic rays, etc. Searches along this line, which are being conducted in the Nuclear Reactions Labor-
atory of the MIR and other laboratories throughout the world, may bring success even if the lifetime of the
superheavy elements is much less than 1010 yr; these objects may prove to be considerably "younger" than
terrestrial specimens.
In a brief discussion of the possible mechanisms of the formation of superheavy elements in processes
of nucleosynthes is in the universe, we may note that the explosions of supernovas have long been regarded as
a fundamental source; during such explosions there takes place what is known as the r-process, a process of
rapid multiple capture of neutrons by nuclei. Although the estimates of the probability and abundance of
superheavy elements obtained as a result of the r-process are highly contradictory [58-60], it remains a pos-
sibility in principle that they can be formed in such a process. Other sources and mechanisms of formation
of supetheavy elements in stellar objects have also been discussed ? pulsars [61], reactions between heavy
nuclei accelerated lathe universe [62], etc.
Thus, in the question of the search for superheavy elements in nature, nuclear physics has yet one more
point of contact with astrophysical problems. There is a curious inverse connection: the problem of the sta-
bility of heavy nuclei, raised by the discovery of spontaneous fission, developing further in the "depths" of
nuclear physics and leading to the prediction of the existence of superheavy elements, may find a solution at
the astrophysical level. In the event of a successful solution, this problem, enriching our ideas on nucleo-
synthesis in the universe, will again return to the field of nuclear physics and give us an answer to the ques-
tion of the fundamental properties of nuclear structure.
Having given a brief introduction to the problem of the search for superheavy elements in nature, we
will not go into a detailed discussion of the results of specific studies ? these have already been reported on
more than once (see, e.g., [63-65]). Instead, using as an example the investigations conducted during the
past 10 years in the Nuclear Reactions Laboratory of the JINR, we describe one of the possible ? and, in our
opinion, successful ? approaches to the search for superheavy elements in nature [66-68].
We are referring to the search for superheavy elements in meteorites of the carbonaceous and non-
equilibrium chondrite type, in which, according to indirect indications, the presence of such elements is most,
probable. In experiments aimed at discovering infrequent events of spontaneous fission, use has been made of
detectors of the multiple emission of neutrons on the basis of proportional counters with 3He, which make it
possible without destruction of the specimen to attain record-breaking sensitivities of 10'15 g/g. (It should
be borne in mind that a method similar in principle to this was used earlier by Libby [5] and Pose [7] for de-
tecting spontaneous fission in uranium. The sensitivity of the method has been improved since that time by a
factor of 107). Measurements were made in a salt mine at a depth of 1100 m of water equivalent. In order to
suppress the cosmic background, the detector was surrounded by a sheath of Geiger counters connected for
anticoincidence. The average neutron-recording effectiveness was 12-30% for various detectors. Special
attention was paid to the problem of background from the spontaneous fission of 238U and of technogenic trans-
uranium isotopes.
After many months of measurements on specimens from the Saratov, Efremovka, and Allende meteor-
ites, researchers observed a multiple-neutron-emission effect, the explanation of which required the assump-
tion that the specimens contained a new long-lived spontaneously fissionable nuclide [66-68], most probably
belonging to the region of superheavy elements.
It is difficult to suppose, however, that superheavy elements can be present only in meteorites; most
likely, it is merely a question of their concentration. Therefore it is by no means impossible that other ob-
jects may prove to be very promising lathe search for heavy elements ? in particular, objects of terrestrial
origin, such as the geothermal waters of the Cheleken peninsula (in the southern Caspian region), Armenian
basalts, etc.
One of the first objects of terrestrial origin on which an intensive search for superheavy elements was
conducted was the geothermal water of Cheleken, which the JINR Nuclear Reactions Laboratory began working
on some years ago. Water from the geothermal source was passed through a large column with an anion-
exchange resin. The mineral fraction was then washed off and placed in the sensitive area of a neutron detec-
tor. The investigators recorded 160 events, of which only six can be attributed to spontaneous fission of the
uranium impurity in the specimens. If, as in the case of the meteorites, we assume that the observed effect
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is due to the spontaneous fission of a long-lived nuclide belonging to the region of superheavy elements, then
Its concentration in the mineral fraction of the resin can be estimated at 2 .10-13 g/g, and the half-life is
assumed to be i09 yr.
One of the methods of identifying a new radiation emitter by the methods of nuclear physics was pro-
posed by Yu. Ts. Oganesyan: when a target obtained by chemical enrichment [66] and containing the element
under investigation is bombarded with a beam of a particles, induced fission can be observed in it. The fis-
sion will take place with a frequency 106 as high as spontaneous fission. As calculations have shown, varyirg
the energy of the a particle, on the basis of the fission-reaction threshold, we can determine the atomic
number of the fissioning nucleus to within two units if the monochromaticity of the beam is no worse than 150
keV.
Similar experiments are being conducted today in Dubna on the U-200 cyclotron, on which it has been
possible to obtain a beam of a particles (LiE = 60 keV) with an energy value smoothly varying from 24 to 40
MeV. As was shown in preliminary experiments, this method makes it possible to detect nuclei of superheavy
elements if the number of such nuclei in the target is 5 .108. Making use of this method, it will be possible
to carry out one of the mot rigorous and critical checks of whether a new spontaneously fissionable natural
radiation emitter is in fact a superheavy element.
The search for superheavy elements has been conducted on specimens of terrestrial and cosmic origin
by various methods in various laboratories all over the world, but until very recently it has been unsuccess-
ful. Repeated announcements of the discovery of superheavy elements have all, on closer examination, proved
to be premature. However, on the basis of the most recent results [66-68], it seems to us that the question
of the existence of superheavy elements in nature has by no means been exhausted, and the search for more
promising natural objects of a new type in combination with the continuous improvement in the sensitivity of
experimental methods gives reason to hope for success in the final solution of this very important problem.
A second line of research is, of course, the artificial synthesis of superheavy elements in reactions be-
tween complex nuclei. Such studies have been conducted since the late 1960s both in Dubna and in other labora-
tories throughout the world, making use of various experimental methods and various beams of accelerated
ions. Researchers have also used diverse approaches to the problem of obtaining superheavy nuclei on heavy-
ion accelerators; however, the many attempts made thus far have not yet brought the desired results. With-
out discussing in detail any specific attempts (this has been done, e.g., in [69, 70]), we will nevertheless point
out that investigations on the artificial synthesis of superheavy elements have substantially deepened our ideas
about the mechanism of interaction between two complex nuclei; e.g., they have led to the discovery of a new
class of nuclear reactions ? reactions of deep-inelastic transfer ? and have provided an exceptionally power-
ful stimulus for the development of many new ideas in heavy-ion physics.
Until recently, all the experimental attempts to synthesize superheavy elements in nuclear reactions
have yielded only the upper bounds of their cross sections of formation. From these data, with certain assump-
tions, we can make estimates of the limiting values of the lifetimes of superheavy nuclei, usually related to
spontaneous fission. However, as has already been noted, the half-life with respect to spontaneous fission is
determined not only by the structure of the barrier but also by the dynamic aspects of the process, in parti-
cular by the mass coefficient. Therefore, on the basis of the limiting values of the lifetime with respect to
spontaneous fission it is difficult to draw any definite conclusions concerning the fission barriers of super-
heavy nuclei. The foregoing relates to spontaneous fission.
However, Oganesyan and his co-workers [71, 72] have recently proposed another approach to the prob-
lem of the artificial production of superheavy elements. It was assumed that the fission barriers exist in
excited nuclei as well, to the degree that the shell effects persist as the temperature and angular momentum
of the nucleus increase. Therefore it may be supposed that for an excitation energy -20-30 MeV the shell
effects in the nuclei are still quite pronounced, and this must have an influence on their disintegration charac-
teristics. Thus, the question of the character of the fission of weakly excited superheavy nuclei may be re-
lated in principle to the presence of a fission barrier in these nuclei. Superheavy nuclei with relatively low
excitation energy E* - 20-40 MeV can be obtained in reactions with ions heavier than argon (see [29,32]).
Taking advantage of this possibility, Oganesyan and his co-workers studied the mass and energy distri-
butions of the products formed in nuclear reactions when 288Pb is bombarded with 48Ca ions having energies of
220 and 250 MeV, and also when 243AM is bombarded with 40Ar ions in the 214-300 MeV energy range [71,72].
In the case of the 288P, + 48Ca reaction the mass distribution of the fission fragments of the compound nucleus
turned out to be asymmetric for E* = 25 MeV, which indicates that the shell effects persist in the nucleus of
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10
-o
.2
1
1
I
60 100 120 140 160
50
100
150
200
Af
Fig. 3. Fig. 4.
Fig. 3. Mass distribution of fission fragments from the compound nucleus 256102 at exci-
tation energies of 25 MeV (0) and 53 MeV (V). The histogram and the dashed curve repre-
sent the distributions of spontaneous-fission fragments for the isotopes 252102 and 256F m,
respectively.
Fig. 4. Mass distribution and angular anisotropy of the products of the 243A M + 46.Ar reac-
tion at energies of 214 MeV (*) and 300 MeV (0).
256102 at this excitation energy. As the excitation energy increases to 50 MeV, the mass distribution of the
fragments becomes practically symmetric (Fig. 3).
While the mass distribution in the first case was determined by a radiochemical method, the energy and
mass distribution for the products of the 213A M + 40Ar reaction were measured on an ion beam, making use of
a pair of semiconductor detectors, the angle between which was uniquely determined from the kinematic condi-
tions and distinguished cases of complete transfer of impulse to the two fragments (two-particle process). It
was found that at an argon-ion energy of 300 MeV a wide distribution of reaction products is observable, in-
cluding the region from 60 to 220 amu and having the shape of a symmetric curve with a maximum near (A ion +
Atarget)/2 ? 140 (Fig. 4), as might have been expected for the fission of an excited compound nucleus. How-
ever, as the energy of the bombarding ions decreases to 214 MeV and the excitation energy correspondingly
decreases to 40 MeV, the most probable event seems to be strongly asymmetric fission with a fragment mass
ratio A heavy/A light ? 2.5, the heavy fragment having a mass of 200-210 amu. Apparently the asymmetric
nature of the fission for an excitation energy of 40 MeV is a consequence of the occurrence of shell effects,
which in the present case are related to the magic numbers Z = 82 and N =126 (268Pb).
From all of these investigations it appears that the mechanism of fission of a weakly excited superheavy
nucleus with Z = 113 and A = 283 is subject to a substantial influence from shell effects. Therefore, it will be
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of great interest in the future to study other combinations of ions and targets leading to the formation of heavy
and superheavy compound nuclei over a wide range of Z and N. Such investigations may be of very great sig-
nificance for the solution of the problem of artificial synthesis of superheavy elements.
CONCLUSIONS
During the time since 0. Hahn and F. Strassmann first observed the fission of uranium under the action
of neutrons, an enormous amount of work has been done on the study of this phenomenon. Researchers have
not only obtained new experimental information but also made a number of discoveries each of which made it
possible to look at the problem from a new and sometimes unexpected viewpoint and substantially affected our
Ideas about the structure of the nucleus and the mechanism of fission in particular.
Perhaps it was no accident that the classical experiments of Hahn and Strassmann on the radiochemical
detection of the products of interaction of neutrons with uranium nuclei were conducted in Germany and not
elsewhere and that Line Meitner was able to give them a correct interpretation which differed so strongly from
the generally accepted ideas about nuclear reactions. Meticulousness and finickiness in the formulation of
experiments and boldness in the explanation of the results ? a successful combination of the concrete and the
abstract that is characteristic of the German school of physics ? occupy an important place among the cir-
cumstances that led to the discovery of fission in these early days.
While a uranium nucleus absorbing a neutron gains an excitation energy -6 MeV and the process of fis-
sion of the excited compound system becomes highly probable, spontaneous fission starts from a state with
zero excitation energy and therefore is an incomparably more infrequent event. However, the observation of
spontaneous fission and its comparison with induced fission have made it possible to explain how the excitation
energy of the nucleus affects the probability and other characteristics of the fission: while the lifetime of
uranium with respect to spontaneous fission is -1023 sec, when we pass to superbarrier fission, as is now
shown by direct measurements making use of shadow effects (see, e.g., [73]), it decreases to -10-16 sec,
i.e., by 39 orders of magnitude.
The development of investigations on spontaneous fission, the entire course of which reflects the bene-
ficial influence of the traditions of the scientific school of the Leningrad Physicotechnical Institute and the
Radium Institute, the style and methods of I. V. Kurchatov's scientific activity ? giving keen attention to new
and sometimes even collateral effects, constantly improving experimental methods, increasing their sensitiv-
ity - have led to the discovery of a number of new phenomena. The discovery of spontaneously fissionable
isomers, e.g., made it possible to study the fission of nuclei with an excitation energy of 2-3 MeV, character-
ized by anomalously large deformation. Of great interest was the phenomenon of delayed fission [74], starting
from a state with an excitation energy comparable to the height of the potential barrier. Here the excitation of
the nucleus arises as a result of the weak interaction ? /3 transition ? and in magnitude it is intermediate be-
tween those taking place during fission from the isomeric state and those taking place under the effect of slow
neutrons. These new effects have "filled in" the excitation-energy interval from zero to -6 MeV and the de-
formation interval from equilibrium deformation to deformation that is twice as great. It should also be noted
that a useful supplement to this picture was provided by experiments on deep subbarrier photofiss ion [75, 761,
which realized the possibility of smooth variation of the excitation energy of the fissioning nucleus. All of
this, in general, has substantially deepened our ideas concerning the stability of heavy nuclei with respect to
fission and concerning the mechanism of the process.
The fission process lies at the base of the nuclear chain reaction, the mastering of which has fundamen-
tally altered the face of our times. In the Soviet Union, work aimed at mastering the chain reaction was begun
under the leadership of I. V. Kurchatov even before the war, and this was decisive in the solution of the ex-
tremely important problems involved in the creation of the well-known structures that guarantee the peaceful
development of the socialist countries. There is reason to think that the experience gained in conducting basic
research, the success of which is usually determined by the possibility of establishing installations whose
qualitative level exceeds the level of contemporary technology, has played a significant role in this respect.
After the solution of the problems of importance to the state, it was natural for the people participating
In this work to tackle the extremely complex theoretical problems of basic nuclear physics. It was possible
to bring into the investigations that style and those scales of effort that were characteristic of the scientific
and organizational activity of I. V. Kurchatov. In particular, with his warm support, work was begun in 1954
on the synthesis of new elements: first the transuranium, then the transfermium, and finally, during the last
decade, the superheavy elements.
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As the basis for the method of synthesizing new elements, Soviet researchers took reactions between
complex nuclei: although in the United States work was still actively being conducted at that time on the pro-
duction of new transuranium elements in high-density neutron fluxes, it became clear that a theoretical break-
through was not to be expected along that line.
The installation chosen for obtaining multicharge ions was the cyclotron. Its "heart" ? the source of
multicharge ions ? was designed essentially by Ac,ademician L. A. Arts imovich in the course of the solution
of problems involving the effective separation of isotopes.
The choice proved to be the right one: for the past 17 years the U-300 cyclotron hasP been a leader
among the heavy-ion accelerators of this generation in the basic parameters of its accelerated-particle beams.
We have already said a good deal about the results obtained in the synthesis of new elements and the in-
vestigation of the actual mechanism of spontaneous fission, which proved to be considerably more complex
than had been supposed in those early pre-war years.
The study of spontaneous fission ? a new type of radioactivity whose discovery is closely linked to the
name of I. V. Kurchatov ? is developing at a rapid rate. We have tried to describe for our reader the main
landmarks on the almost 40-yr path along which we and many other physicists have advanced in our investiga-
tions and to give an idea of its future prospects. It may be that a few years from now we will look back and
smile at our present ideas on the question in what direction and just how the future development of these in-
vestigations will proceed. One thing is beyond question: the place occupied by spontaneous fission not only in
nuclear physics but also in related fields of knowledge is a guarantee of unflagging interest in this phenomenon.
The fate of the is land of stability of superheavy nuclei, the possible existence of a new region of elements in
Mendeleev's periodic table, and many other aspects of nuclear physics depend almost entirely on how strongly
subject to spontaneous fission are the nuclei which were at first merely a dream and have now become an ob-
ject of experimental investigation.
The present-day situation with regard to the search for superheavy elements is surprisingly reminiscent
of the events preceding the final discovery of spontaneous fission. Only 1 year ago, we were able to observe
no more than a few events of spontaneous fission of a new natural nuclide per year. Thanks to the constant
improvement of methods of search, enrichment, and identification, today we are recording several spontan-
eous fissions every day. Just as it did 40 years ago, the discovery of the truth requires many highly diverse
and perhaps even more laborious control experiments. Furthermore, at the time of the first experiments on
spontaneous fission very little was known concerning induced fission. Today we have a scarcely better idea
of the possible properties of superheavy elements. Therefore, notwithstanding the enormous effort already
expended in the attempts to discover or synthesize superheavy elements, even greater efforts will have to be
made.
However, we hope that this next turn of the spiral along which nuclear physics is developing will lead in
any case to a deeper understanding of the fundamental properties of matter.
LITERATURE CITED
1, 0. Hahn and F. Strassmann, Naturwiss., 27, No. 11, 89 (1939).
2. L. Meitner and 0. Frisch, Nature, 143 (1939), p. 239.
3. Ya. I. Frenkel', Zh. Eksp. Teor. Fiz., 2, No. 6, 641 (1939).
4. N. Bohr and J. Wheeler, Phys. Rev., 56, 426 (1939).
5. W. Libby, ibid., ??? 1269.
6. K. A . Petrzhak and G. N. Flerov, Dokl. Akad. Nauk SSSR,
1013 (1940); J. Phys., 1, 275 (1940).
7. H. Pose, Z. Phys., 121, 293 (1943).
8. K. A. Petrzhak and G. N. Flerov, Usp. Fiz. Nauk, :71, No. 4,
9. L. Z. Malkin, I. D. Alkhazov, A. S. Krivokhatskii, and K. A.
(1963).
10. B. M. A leksandrov, A. S. Krivokhatskii, L. Z. Malkin, and K.
(1966).
11. L. Z. Malkin et al., ibid., 1.5? No. 2, 249 (1963).
12. I. D. Alkhazov et al., Yad. Fiz., 11, No. 3, 501 (1970).
13. I. D. Alkhazov et al., ibid., iS, No. 1, 22 (1972).
14. I. Alkhazov et al., in: Proceedings of the Second IAEA Symposium on Physics and Chemistry of Fission,
Vienna, IAEA-SM-122/150 (1969), p. 961.
500 (1940); Zh. Eksp.
Teor. Fiz., 10,
655 (1961).
Petrzhak, At. Energ., .11, No. 2, 158
A. Petrzhak, ibid., 2.2, No. 4, 315
30
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15, V. M. Adamov et al., Yad. Fiz., 13, No, 5, 939 (1971).
16. V. M. Adamov et al., ibid., 5, No. 4, 923 (1967).
17. L. Z. Malkin et al., At. Energ., 16, No. 2, 148 (1964).
18. V. M. Adamov et al., Yad. Fiz., 5, No. 1, 42 (1967).
19. V. M. Adamov, S. S. Kovalenko, K. A. Petrzhak, and I. I. Tyutyugin, ibid., 9, No. 4, 732 (1969).
20. V. M. Adamov et al., ibid., 11, No. 5, 1001 (1970).
21. V. M. Adamov et al., Izv. Akad. NaukSSSR, Ser, Fiz., 37, No. 1, 118 (1973).
22. B. M. A leksandrov et al., in: Neutron Physics (Proceedings of the Third All-Union Conference, Kiev,
1975) [in Russian], Part 5, Atomizdat, Moscow (1976), P. 166.
23. 0, I. Batenko et al., ibid., p. 114.
24. M. V., Adamov et al., in: Problems of Atomic Science and Technology [in Russian], "Nuclear Constants"
Series, No. 24, Atomizdat, Moscow (1977), p. 8.
25. G. Flerov, in: Proceedings of the Conference on Reactions between Complex Nuclei, Gatlinburg, Oak
Ridge (1958), ORNL-2606, p. 384.
26. G. N. Flerov, Proceedings of the Second International Conference on the Peaceful Uses of Atomic
Energy, Geneva, 1958 [in Russian], Vol. 1, Gosatomizdat, Moscow (1959), p. 272.
27. G. N. Flerov, V. A. Druin, and A. A. Pleve, Usp. Fiz. Nauk, 100, No, 1, 45 (1970).
28. G. N. Flerov and I. Zvara, JINR Report D7-6013, Dubna (1971).
29. Yu. Oganessian, A. Demin, A. Iljinov, and S. Tretyakova, Nucl. Phys., A239, 353 (1975).
30. Yu. Ts. Oganesyan et al., Pis'ma Zh. Eksp. Teor.Fiz., 20, No. 8, 580 (1974).
31. Yu. Oganessian et al., Nucl. Phys., A273, 505 (1976).
32. G. Flerov et al., ibid., A267, 359.
33, V. V. Volkov, EChAYa, 2, No. 2, 287 (1971).
34. V. V. Volkov, ibid., 6, No. 4, 1040 (1975).
35. V. A. Karnaukhov, ibid., 4, No. 4, 1018 (1973).
36. D. Bogdanov et al., Nucl. Phys., A275, 229 (1977).
37. K. G. Kaun, in: Proceedings of the International School and Seminar on the Interaction of Heavy Ions
with Nuclei and the Synthesis of New Elements [in Russian], JINR, D7-9734, Dubna (1976), p.245.
38, G. N. Flerov, in: Proceedings of the Fifth International Conference on Charged-Particle Accelerators
[in Russian], JINR, Dubna (1977).
39. G. N. Flerov, JINR Preprint R7-7551 [in Russian], Dubna (1973).
40. W. Whitehouse and W. Galbraith, Nature, 169, 494 (1952).
41. G. Seaborg, Phys. Rev., 85, 157 (1952).
42. Yu. Oganessian et al., Nucl. Phys., A239, 157 (1975).
43. W. Myers and W. Swiatecki, ibid., 81, 1 (1966).
44. S. Johansson, lid., 12, 449 (1959).
45. S. Johansson, ibid., 22, 529 (1961).
46. S. M. Polikanov et al., Zh. Eksp. Teor. Fiz., 42, 1464 (1962).
47. S. M. Polikanov, Isomerism of the Shape of Atomic Nuclei [in Russian], Atomizdat, Moscow (1977).
48. G. N. Flerov and V. A. Druin, in: Structure of Complex Nuclei [in Russian], Atomizdat, Moscow
(1966), p. 249.
49. V. Strutinsky, Nucl. Phys., A95, 420 (1967); A122, 1 (1968).
50. M. Brack et al., Rev. Mod. Phys., 44, 430 (1972).
51, Yu. A.Muzychka, V. V. Pashkevich, and V. M. Strutinskii, JINR Preprint R7-3733 [in Russian],
Dubna (1968).
52. S. Nilsson et al., Nucl. Phys., A115, 542 (1968).
53. S. kTilsson, S. Thompson, and S. Tsang, Preprint UCRL-18531, Berkeley, California (1968).
54. T. Ledergerber and H. Pauli, Nucl. Phys., A207, 1 (1973).
55. J. Randrup et al., ibid., A217, 221.
56. J. Randrup etal., Phys. Rev., C13, 229 (1976).
57. A. Sobiczewski, Physica Scripta, 10A, 47 (1974).
58. P. Seeger, W. Fowler, and D. Clayton, Astrophys. J. Suppl., 11, 121 (1965).
59. E. E. Berlovich and Yu. N. Novikov, Pis'ma Zh. Eksp. Teor. Fiz., 9, 445 (1969).
60. D. Schramm and W. Fowler, Nature, 231, 103 (1971).
61. G. Silvestro, Lett. Nuovo Cimento, 2, 771 (1969).
62. M. KowaLs.ki and B. Kuchowich, Phys. Lett., 30B, 79 (1969).
63. G. Flerov, in: Proceedings of the Fourth International Conference on Peaceful Uses of Atomic Energy,
Geneva, 1972, Vol. 7, Vienna, IAEA (1972), p. 471.
31
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64. G. Flerov, in: Proceedings of the International Conference on Reactions between Complex Nuclei, Vol.
2, Nashville, USA (1974), p. 459.
65. G. Herrmann, Int. Rev. Sci. Ser. 2 ? Inorganic Chemistry, Vol. 8 ? Radiochemistry, p. 221, Uni-
versity Park Press, Baltimore (1975).
66. G. N. Flerov et al., Yad. Fiz., 26, No. 3, 449 (1977).
67. I. Zvara et al., ibid., 455.
68. G. N. Flerov, Superheavy Elements [in Russian], Report at the International Conference on Nuclear
Structure, Tokyo, Sept. 1977.
69. G. N. Flerov, JINR Preprint R7-9956 [in Russian], Dubna (1976).
70. Yu. Oganessian, Nukleonika, 22, No. 1, 89 (1977).
71, R. Kalpakchieva et al., JINR Preprint E7-10587, Dubna (1977).
72. R. Kalpakchieva, Yu. Oganessian, Yu. Penionzhkevich, and H. Soban, Zeitschrift fiir Physik, A283,
No, 3, 253 (1977).
73. S. A. Karamyan, Yu, V. Melikov, and A. F. Tulinov, iChAYa, 4, No. 2, 456 (1973).
74. V. I. Kuznetsov, N. K. Skobelev, and G. N. Flerov, Yad. Fiz., 4, 271 (1966).
75. C. Bowman, I. Schr6der, C. Dick, and H. Jackson, Phys. Rev., 12C, 863 (1975).
76. V. E. Zhuchko et al., Pistma Zh, Eksp. Teor, Fiz., 22, 255 (1975).
ISOMERS IN THE MILLISECOND REGION
A. P. Klyucharev, V. V. Remaev, UDC 539.163.546.794
and Yu. N. Rakivnenko
Nuclear isomers have provided a subject of constant interest at all stages of the research into the struc-
ture of atomic nuclei. From a theoretical viewpoint, the interest in isomeric nuclei is associated with the in-
vestigation of intranuclear processes leading to the formation of long-lived excited states and with the deter-
mination of the level of prohibition for the corresponding decay channels; from a methodological viewpoint,
isomers are a convenient means of investigating processes of very short duration that occur within the nucleus.
In addition, the lifetime of nuclei in isomeric states may be sufficient to allow the practical use of isomers
with given special properties.
The study of isomeric states and their decay has played an important part in the development of current
theoretical models of atomic nuclei. Its contribution is widely known: the uniform distribution of long-lived
isomers over N or Z (isomer islands) agrees with the shell structure of single-particle nucleonic models in
nuclei; the generalized model of the nucleus is confirmed by the existence of a strong prohibition on asymp-
totic quantum numbers; the discovery of fissioning isomers offers a unique opportunity for the investigation
of large nuclear deformations and for fission physics. At present, the interest in isomers is not only growing
but is extending to more fundamental matters: the search for density isomers, rotational isomers, etc.
Broad research into nuclear isomers began in [1], where the excitation of isomeric states in the products
of nuclear reactions was first shown to be possible. In [2] a historical account is given of the discovery of iso-
mers of artificially radioactive nuclei, while in [3] there is a discussion of the importance of the pioneer work
in this field carried out over a period of 30 years in I. V. Kurchatov's laboratory and, in particular, the con-
stant interest in this topic generated by Kurchatov in the country's research institutes.
Kurchatov's research on the decay of the isomer "InBr may be regarded as the starting point for one of
the important research topics in current nuclear physics: nuclear spectroscopy using nuclear reactions. In
the work on "InBr it was shown that radiative transitions in the nucleus or internal electron conversions form
an important decay channel for isomeric states and the multipolarity of the isomeric transition was determined
by measuring the internal-conversion coefficients [4].
Nuclear reactions provide the most universal and at present also the principal means of investigating the
structure of excited nuclear states. However, because of the complexity of the radiation accompanying the de-
cay of the reaction products spectroscopy in a beam of bombarding particles poses difficult methodological
problems. Until precision semiconductor radiation detectors are developed, spectroscopic investigation is
Translated from Atomnaya i'lergiya, Vol. 44, No. 1, pp. 36-44, January, 1978.
32 0038-531X/78/4401-0032 $07.50 01978 Plenum Publishing Corporation
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750
500
250
0
200
1500
1000
500
g 0
150
1000
500
200
1500
1000
500
_
_
x
6
1
44111/41i*
1
INV(
a
?
174
1r /98,7jGern
538
1
T 668
1 773
b
-
c
I
."'"A. ?
I
vA-^,--........?......,??,.... ,
11
'414.PIL14161141.4***410"`Ae
ci
0 500
y energy, keV
Fig. 1. 7 spectra of decay of millisecond isomer 132mXe
(To = 8.7 msec). Analyzer time mode with duration 6.4
msec (a) and 51.2 msec (b, c, d).
250
750
only possible in certain special cases. For example, the large cross section of (n, 7) reactions for a number
of rare-earth isotopes has enabled L. V. Groshev and co-workers to complete a large program of research on
this topic; light nuclei with a relatively simple energy-level structure have been studied in (p, 7) and (p, ny)
reactions at the Kharkov Polytechnical Institute (KPI), where (a, xn) reactions have been effectively used to
investigate the lower rotational state in deformed nuclei.
The search for millisecond isomers began in the mid-1950s, on the initiative of 0. I. Leipunskii. In-
vestigations were carried out at the Institute of Chemical Physics of the Academy of Sciences of the USSR
using a 14-MeV neutron beam and at KPI using a linear proton accelerator with a maximum energy of 20.8
MeV. At first, the abundance of isomers of lifetime 10-4-101 sec and the probability of their excitation in
nuclear reactions were the main centers of attention.
A large number of isomers were found in the millisecond-lifetime range; several of these are of high
excitation energy and hence sufficiently high spin. Thus, it is possible to investigate the properties of excited
nuclear states in the region inaccessible for investigation by radioactive isotopic decay.
33
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Fig. 2. Apersin-type 13 spectrometer: 1) height
regulation; 2) diffusion pump; 3) side vacuum
valve; 4, 6) target holder; 5) central vacuum
valve; 7) lens body; 8) coil of toroidal lens; 9)
vacuum jacket; 10) Pb shield; 11) support; 12)
regulation in horizontal plane; 13) rotational track.
(The arrows indicate possible paths of the acceler-
ated-particle beam to the target.)
1800 2000 2200 - 3600 3800 4000
4600 4800 Hpy Oe ? cm
Fig. 3. ICE spectra of isomers: 0) 138mCe (To = 8.6 msec); ?)
139mCe (T1/2 = 60 sec), obtained in the reaction (a, 3n). The spec-
trum of inCe was obtained in the second recording interval, begin-
ning 100 msec after the beam pulse, and subtracted from the read-
ings obtained in the first recording interval (of equal duration), be-
ginning 1 msec after the current pulse.
Measurement Procedure
The activation method or the de layed-collis on method cannot be used to investigate nuclei with half-life
T1/2 =10-6-1.0 sec. In this case, an effective method is pulse irradiation of a target, recording the radiation
in the intervals between accelerator current pulses.
In the present work, a linear proton accelerator with energy E p = 20.8 MeV and a linear a particle
accelerator with energy Ea = 38 MeV were used. The pulse-repetition frequency of both the accelerators was
34
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TABLE 1. Isomers with Lifetimes of 10-4-10-1 sec
Isomer
Reaction
T112,msee
Isomer-
state energy.,in
MeV
Energy and
rmanPolaritY
of isomer
transition
Liter-
attire
source
43Sc
41K(a, 2n)
aoca (a, p)
0,45
0,15
3/2+
0,15; M2 -
[22]
46V
7iGe
46Ti (p, n)
71Ga (p, n)
1,0
0,96
72Ge.(p, pn)
.
Zn (a, xn)
22,4
0,198
9/2+
0,024; M2
69Ga (a, pn)
72Ge (a, an)
791is
78Ge (p, 2n)
0,305; E3
75A8(P, p')
17,1
0,305
9/2+
[23)
75As (a, a')
0,025; M2
78Br
tiainly
79As(a, n)
88Sr (p, n)
0,145
0,181
4+
? 0,15; M2
[24]
89Y (P, /m)
Rb (a, xn)
86Sr (a, pn)
14,8
0,673
8+
0,442; E3
89Y (a, an)
88 m2y
87Rb (a, 3n)
0,3
0,393
1+
0,393; E3
[25]
90Nb
99Zr (p, n)
891" (a, 3n)
6,5
0,382
1+
. 0,256; E3
totTe
maitu
98Mo (a, p)
momo (a, n)
104Ru(a, an)
0,8
1,8
0,19
0,21
5/2-
0,19; M2
[22]
[22]
091n
i"Ag (a, 2n)
215
2,11
19/2+
0,68; M3
[26]
114In
114Cd (p, n)
42
0,5
8-
0,311; E3
1241
118Sn
Cd (a, zn)
ii8Sii (a, an)
0,155
0,725
11/2-
0,107; M2
[27]
114Sb
ii4Sn (p, n)
0,23
Ii2Sn (a, pn)
117Sb
"51n (a, 2n)
0,35
3,13
25/2+
0,058; M2
[28]
ttvre
122j
Sri (a, :cn)
121Sb (a, 3n)
101
0,07
0,3
0,5
[29]
132Xe
1-28Cs
139Te (a, 2n)
1271(a, 3n)
8,9
4,4
2,754
0,071
10+
0,537; E3
[30]
131La
138La
13213a (p, 2n)
138Ba (p, n)
0,16
0,17
.137Ba(p, 2n)
133Cs (a, n)
100
0,096
137La
'Ba (p, 2n)
12
1,1
138Ce
139La (p, 2n)
Ba (a, zit)
8,65
2,126
7-
0,302; E3
14?Nd
igpm
'41Pr (p, 2n)
138Ce (a, 2n)
1411sId (p, n)
0,6
2,2
7-
0,43; E3
143Nd (p, 2n)
141Pr (a, 3n)
2,28
0,885
8-
0,435; E3
146Eu
147Sm (p, 2n)
0,24
193Gd
Sm (a, xn)
0,08
0;12
[31]
188Gd
193Tb
194Sm (a, 3n)
Ga (p, 2n)
30,8
0,18
0,122
0,08
11/2-
0,014; El
[31]
191Eu (a, 2n)
0,118; M1
159Dy
Ga (a, xn)
0,14
0,356
11/2-
0,218; E2 -
[32]
0,09; M1
inLu
'"Yb (p, 2n)
0,45
0,133
1-
0,07; El
178Ta
1781,u (a, 3n)
1,1
1
180W
181Ta (p, 2n)
5,6
1,530
8-
0,39; El
Hf (a, xn).
183Re
18iTa (a, 2n)
0,82
1,907
25/2*
0,194; E2
[33]
itros
18.1Ir
W (a, zit)
1880s (p, 2n)
0,24
0,157
5/2+
0,157; M2
[34]
i85Re (a, .3n)
30
0,187
9/2-
0,187; E3 ?
0,077; M2
188Ir
187Re (a, 3n)
4,0
189Ir
1990s (p. 2n)
13,4
0,372
11/2-
0,72; M2
187Re (a, 2n)
0,258; E3
i 92a, 'Au
191Ir (a, 33)
32,5
0,135
5+
0,63; M2
0,103; E3
192,a2A?
191Ir (a, 3,i)
164
0,431
11-
0,06; E3
194m,Au
193Ir (a, 3n)
600
0,092
5+
0,011; M2
0,056; E3
194m2A,
'931r (a, 3n)
39,2
0,46
11-
0,07; E3
199T1
zooHg(p, 2n)
27,8
0,749
9/2-
0,382; E3
[35]
197Au(a, 2n)
201T1
2011.1g (p, n)
1,8
0,93
9/2-
0,23; /1/2
2991-Ig (p, 2n)
0,6; E3
204miBi
203T1 (a, 3n)
13
0,806
10-
0,752; E3
2o4m2Bi
293T1 (a, 3n)
1,07
2,793
16+
0,275; E3
206Bi
299T1 (a, 3n)
0,89
1,044
10-
0,905; E3
207Bi
298T1(a, 2n)
0,2
2,1
21/2+
0,743; E3
[34]
0,456; E3
205m1p0
204pb (a, 3n)
57
1,46
19/2-
0,58; E3
205 m2po
204pb (c,, 3n)
0,64
0,88
13/2+
0,161; M2
*The works cited describe investigations of the Isomers at KPI and not necessarily the
first observation of the isomers.
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? E, MeV 3,5404 sec
206
ES 419
1,87
48!
EZ
1,06
E2
081
13680
56 80
7-
24.
if, MeV
4/282
1,8262
476'88
8,610 sec if, MeV 06.10-J sec .7
2,20 ? 7_
ES
43022
E2
1,0376
E2
0,7888
7-
4+
0 C+
, 138 c
58c 86
7,77
0,77
ES
0,43
E7.
100
E2
477
740
2+
Fig.
Fig. . Decay of two-particle isomeric states in even?even nuclei with 80 neutrons.
E,keV 11,7 sec .75K
1035 93E1 8-8nn
s
945 ? 80
556
389
EZ
6+0
289
E2
267 4+0
185
E2
822+0
, 82 E23

E, keV
1480
1148
1060
633
331
111
4,86
18.9 El
427
E2
326
E2
tr8nn
8-8pp
840
6+0
5.35 z
E,keV K
1529,2 msec 5-8m7
390,7
El
1138,5
688,1
336,6
450,4
E2
351,5
E2
317 4+0 233,9
214 E2
E2
E2
93
2.0 7027 1 ro
102,7 1 127
127 ro 162
o '7/1/ 93E2 0,0 E2E2
0 0'O *0 0
176 Yb
70 105 18752 ()so
77782"106 180 W
74 106 18785, Pt
Fig. 5. Decay of two-particle isomeric states in even?even deformed 'nuclei
with 106 neutrons.
8+0
5"0
4+0
0.8 1.0
6, keV msec grK E, keV msec 7-"K
1830 8-8nn 1836 8-8n6
1277
793
400
553
El
484
E2
394
E2
273
8+0
1226
5V 795
4+0
434
162
610
El
437
E2
351
?2
272
E2
8+0
6'0
4'0
2+0
2 sec-1, with a pulse length -500 psec These target-irradiation conditions ensured high selectivity in iso-
lating the millisecond-isomer decay spectrum from the intense and complex y radiation accompanying the
decay of the reaction products formed with protons and a particles at these energies. "Instantaneous" radia-
tion from the target was eliminated by obstructing the detector and the recording equipment during the irradia-
tion, and the contribution due to the radioactive decay of the isotopes produced in the reactions was taken into
account by time analysis of the spectra, which was facilitated by the half-life (>1 sec) of the background activ-
ity. This method allowed the decay of isomers with formation cross section al mb to be investigated against
a background of activity with excitation cross section 1 b.
All the stable elements from carbon to bismuth (except the rare gases) were irradiated by protons and
an a-particle beam. Information required for further investigations was obtained, regarding the background
conditions associated with the use of various constructional materials in the beam path close to the detector
or with the choice of chemical compounds for the targets when pure elements cannot be used. In addition,
appropriate y and f3 emitters for energy calibration of the spectrometers were chosen. The main isomer-
excitation reactions were (p, n), (p, 2n), and (p, pn) for protons and (a, 2n) and (a, 3n) for a particles.
Measurement of Spectra of y Radiation and
Internal-Conversion Electrons
The energy spectrum of y radiation was investigated using a scintillation NaI(T1) spectrometer or a
36
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Declassified and Approved For Release 2013/03/07: CIA-RDP10-02196R000700110001-5
keV
1571, /1 2'53ffisec 10-p(h9/2)In (173/2)-7
E, keV 317
8045, /30ms c 8146 0,69mse910_
1043,6,
E,keV
'/
E, keV //
/
425 0,4sec
E, YeV 7,7sec
10
2445
6 / ////1//////2"( 7 ) O//////),,/,/7----0
1404
40 7*
/7/7
643
/6* '0
Ca
6501 7'
5/0
p(hcipin f1/211
4: 1
p(hvi)
5 n ( py,)
188.
8
115 63
TOO R .
83 '1117
204 .
838'121
206
83 Bil23
208m .
83 Bt.125
Fig. 6. Decay of 10- two-particle isomeric states in odd ? odd bound isotopes.
semiconductor Ge (Li) instrument. At various stages of the investigation an AI-100 single-channel pulse-
amplitude analyzer (with division of the channels into two groups) and an AI-4096 multidimensional analyzer
were used as the recording equipment. In all cases, recordings were made in two or more time intervals.
In the first interval the spectrum of the isomeric y radiation plus the background from long-lived activity was
obtained. This interval follows, with some given delay, an accelerator current pulse of duration equal to 2-5
isomer-activity half-lives, In subsequent intervals (time groups) the longer-lived radiation was recorded.
By this method, the background radiation could be reliably eliminated, or the spectra of several isomers
appearing simultaneously at the target could be separated (Fig. 1).
The spectrum of internal conversion electrons (ICE) was investigated using magnetic analyzers: for the
proton beam a spectrometer with improved focusing [5] and for the a-particle beam a nonferric two-lens spec-
trometer of Apel'sin type (aperture ratio 20% of 4r) [6] (Fig. 2), which allowed (e, e) and (e, y) reactions to
be measured. As in the investigation of y spectra, measurements of the electrons in the /3 spectrometer were
made in two time intervals for each point of the spectrum. The exposure time was determined by monitoring
the beam current. ICE spectra for cesium isotopes are shown in Fig. 3.
The half-lives were measured on multichannel time analyzers. The pulses from the y detector were
E keV
1450
57 msec
644 ?sec
88 0
719
La,
IT
P n
19 h2
2 2/21 /2
13 +
2
2
5
0 I -1
2 512
205D
84r ?
Fig. 7. Decay of isomeric states in 205Po nucleus.
37
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Declassified and Approved For Release 2013/03/07: CIA-RDP10-02196R000700110001-5
2170
? ?
z
2041
5-
thsec
? 71 ( hg/2)11/ (f5/2)-1 V(1:73/2Y
2793,5
2612,2
16+
14-
1623
13-
2519,5
? _
1383
4+
1783
12-
961
Z
r-?-?
11-
7414,5
Z
13msec --
10
--- V ( ( h9/2)1
806,5 ?
202
82
'20
54
7+
V ( f5/2)' IT( h9/2)1
11,3h
204 Bi
83 121
Fig. 8. Dec.ay of high spin (16+) isomeric state in 2G4Bi nucleus.
preliminarily analyzed using a differential analyzer tuned to one of the peaks in the energy spectrum of the
particular isomer. In the case of the ICE spectra, the magnetic analyzer was tuned to one of the conversion
lines.
Identification of Reactions Leading to Isomeric Nuclei
The isotopes responsible for the formation of an isomer state are determined by comparing the yields of
a given activity from targets excited by different isotopes of the same element. The type of reaction leading
to the isomer is determined from the reaction threshold and the form of the excitation function for the given
activity. For certain isomers the atomic number Z is determined from the energy of the x-ray K line (by
absorption in filters [7]) or from the energy difference between K and L conversion lines in the electron spec-
trum.
Table 1 summarizes the results for nuclear isomers with lifetimes in the millisecond range, observed
and studied at KPI.
The detailed study of multiparticle isomeric states with high excitation energy and spin is of particular
interest, in connection with residual nucleon interactions in the atomic nucleus.
From an analysis of the experimental material obtained and the results of other experimenters, it is
possible to identify certain patterns for various groups of nuclei, some of which are illustrated in Figs. 4-8.
Isomers 13 6mBa [9], 13 8mCe, and 14 ornN
a [10]
These isomers belong to a rare group of isomers in even?even nuclei. In this group, the excitation
energy of the isomeric state is relatively large (-2 MeV), the spin and parity are I = r, and decay is by
electric octupole transition to the collective level 4+ (Fig. 4). The appearance of these levels in even?even
nuclei is due to rupture of a neutron or proton pair, with the formation of a two-particle state. In this range
of mass numbers a large nuclear spin may develop as a result of rupture of the neutron pair in the state hio,
when one neutron passes to the level do. In this case the spin of the isomeric state is determined by the con-
figuration ni (h11/2)n2 (do).
Isomers 1 76mYb [11], 1 7 8mHf [12], 180mw [13], 182m05 [1 4 ]
and 1 84mPt [15]
These isomers also belong to a group of two-particle states in even?even deformed nuclei, formed by
the rupture of neutron pairs. The spin and parity of the isomer level is 8- for K = 8 and transition from this
level to the rotational band of the ground state is due to radiation of type El with a strongly hindered prohibi-
tion on the quantum number K (Fig. 5).
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Isomers 2o41111Bi and 2"mBi
In reactions between odd?odd bismuth isotopes with mass numbers 204 and 206 and a particles an
isomeric state with spin and parity VT =1F has been observed and investigated; this state may be attributed
to the particle-vacancy configuration p(h2/2)1n(113/2)-I. As well as these bismuth isotopes, the decay of the
is omers199mBi,2??mBi, and 209mBi [16] is shown in Fig. 6. Isomer states with I =10- were also observed
in 194mBi and 196mBi in [17].
The situation in 202Bi remains unclear. To date, no isomer states with the above characteristics have
been observed, although there exists a neutron-vacancy state n(i13/2)-1 in the 201Pb nucleus.
Isomer 205mP0 [18]
The three-particle isomeric state in the 205Po nucleus with T1/2 = 57 msec was investigated in the reac-
tion 214Pb(a, 3n)205mP0. This state with excitation energy 1460 keV and spin and parity FT =19/2- is discharged
by electric octupole transitions to the 880-keV level (III' =13/2+), which is a single-particle isomeric state with
configuration n(ii3/2)-1 [19].
The three-particle isomeric state in odd isomers of polonium is due to a combination of two-proton ex-
citation of the nuclear core of polonium and single-neutron excitations known in the corresponding lead , iso-
topes (isotones of polonium). Such states are known in 205Po, 207po, 2o9poand211130 [20]. The decay of states
in 205Po is shown in Fig. 7.
Isomer 2"m2B1
In the 214Bi nucleus a four-particle isomeric state with excitation energy 2795 keV and spin and parity
FT = 16+ has been discovered and investigated. It decays by a directed cascade of transitions to the isomeric
state FT =10-. The large spin (16) of this isomer cannot be described by a two-particle configuration because
the interaction of two particles at the level i1312 gives a maximum spin I =12. It was shown in [21] that the
spin 16+ arises as a result of a combination of configurations of two-neutron states in the neighboring even
?even nucleus 1P13120 with configurations responsible for isomers in odd ? odd bismuth isotopes.
It remains to thank A. M. Morozov, V. T. Gritsine, V. A. Lutsik, I. A. Romanii, K. S. Goncharov,
E. A. Skakun, and G. Ya. Yatsenko for direct and active participation in the work.
LITERATURE CITED
1, I. Kurchatov et al., C. R. Acad. Sc, 200, 1201 (1935).
2. L. I. Rusinov, Usp. Fiz. Nauk, 23, 616 (1961).
3. L. I. Rusinov, At. Energ., 5, No. 5, 432 (1958); L. K. Peker, Usp. Fiz, Nauk, 23, 631 (1961).
4. I. V. Kurchatov and L. I. Rusinov, Jubilee Volume Celebrating the Thirtieth Anniversary of the October
Revolution [in Russian], Part 1, Izd. Akad, Nauk SSSR, Moscow (1947), p. 285.
5. Yu. N. Rakivnenko et al., Ukr. Fiz. Zh., 13, No. 3, 478 (1968).
6. Yu, N. Rakivnenko et al., Ukr. Fiz. Zh., 15, No. 4, 578 (1970).
7. V. T. Gritsyna, A, P. Klyucharev, and V. V. Remaev, Yad. Fiz., 3, 993 (1966).
8. Bibliography of Papers Written at the Physicotechnical Institute of the Academy of Sciences of the
Ukrainian SSR 1930-1971 rim Russian], Vol. 1, Kharkov (1972).
9. F. Ruddy and B. Pate, Nucl. Phys., 69, 471 (1965).
10. V. V. Remaev et al., Zh. Eksp. Teor. Fiz., 43, 1649 (1962).
11. M. Vergnes et al., Phys. Lett., 18, 325 (1965).
12. P. Fettweis and E. Campbell, Nucl. Phys., 33, 272 (1962).
13. I. Softky, Phys. Rev, 98, 736 (1955). '
14. J. Burde, R. Diamond, and F. Stephens, Nucl. Phys., 85, 481 (1966).
16. J. Burde, R. Diamond, and F. Stephens, Rep. Lawrence Rad. lab. Chem. (1965).
16. U. Hagemann et al., JINR Preprint E6-6597, Dubna (1972); W. Alford, J. Schiffer, and J. Schwartz,
Phys. Rev., C3, 860 (1971).
17. S. Khoinatski et al., Program and Paper Abstracts for the Thirteenth Conference on Nuclear Spectros-
copy and the Structure of the Atomic Nucleus [in Russian], Nauka, Moscow (1973), p? 115,
18, C Hargrove and W. Martin, Can. J. Phys., 40, 964 (1972).
19. B. Jonson et al., Nucl. Phys., A174, 225 (1971),
20. B. Focke et al., Z. Phys., 259, No. 3, 269 (1973).
39
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Declassified and Approved For Release 2013/03/07: CIA-RDP10-02196R000700110001-5
21. *Va. Rakivnenko et al., Phys. Lett., 44B, No. 5, 62 (1973).
22. k. Brandi et al., Nucl. Phys., 59, 33 (1964).
23. A. Schardt and J. Welker, Phys. Rev., 99, 810 (1955).
24. R.Duffield and S. Vegors, Phys. Rev., 112, 1958 (1958).
25. S. Vegors and P. Axel, Phys. Rev., 101, 1067 (1956),
26. K. Alexander et al., Phys. Lett., 17, 322 (1965).
27. E. Ivanov et al., Nucl. Phys., M, 177 (1964).
28. C. Heiser et al., in: Nuclear Spectroscopy and Nuclear Theory [in Russian], Dubna (1969).
29. A. G. Demin and I. M. Rozman, Zh. Eksp. Teor. Fiz., 45, 2067 (1963).
30. H. Brinckman et al., Nucl. Phys., A96, 318 (1967).
31. J. Borggreen and G. Sletten, Nucl. Phys., A143, 255 (1970).
32. J. Borggreen and Gjaldbaek, Nucl. Phys., A113, 659 (1968).
33. M. Emmott et al., Phys. Lett., 20, 56 (1966).
34. T. Conlon, Nucl. Phys., A100, 545 (1967).
35. R. Diamond and F. Stephens, Nucl. Phys., 45, 632 (1963).
ANNIHILATION AS AN ENERGY SOURCE
N. A. Vlasov UDC 539.1
I. V. Kurchatov discovered for his native land how to use the energy from nuclear transformations.
The progress in nuclear power, which began in his lifetime and under his leadership, has stimulated the
search for new possibilities. The possibility of using annihilation as a fuel process appears to be the most
tempting of all possibilities. You see, a kilogram of annihilating antimatter is equivalent to a ton of nuclear
fuel. The use of annihilation fuel has already been discussed in the technical literature. However, because
of the lack of systematic data about the physical characteristics of the annihilation process, inventive tech-
nical ideas at times go off in unreal directions. The required physical data are either completely unavailable
or scattered throughout a vast set of original papers and reports. Although the outlook for technical use of
annihilation is still far from clear, the search for it will, of course, continue. The known physical character-
istics of annihilation are presented in this paper. They may be useful in selecting a path along which to search
and in limiting unnecessary flights into wild fantasy.
The annihilation of antiparticles in collisions with particles usually turns out to be the conversion of a
pair into lighter or massless (with zero rest mass) particles such as photons. C onsequently ,, annihilation
transforms rest energy either into kinetic energy of particles of lesser mass or into radiated energy which is
transmitted at the speed of light. In the known power processes of combustion and explosion, the same thing
occurs; some portion of the rest energy is converted into heat, i.e., into the kinetic energy of atoms and
molecules. Qualitatively, annihilation is a typical energy process.Quantitatively, it is the most intense.
The specific energy release (heating power) of annihilation is extremely high; rest energy is completely con-
verted into heat and radiation. The most intense of the known processes ? thermonuclear fusion of light
nuclei ? converts only -0.5% of the rest energy. Theoretically conceivable, but as yet unknown, methods for
extraction of gravitational energy by means of bodies such as black holes essentially promise no more than
30% of the rest energy. The outstanding heating power also draws attention to annihilation. Laboratory studies
of annihilation yielded many interesting results in the physics of elementary particles [1]. In nature, the for-
mation and annihilation of pairs takes place on a grandiose scale in all likelihood. For example, it is assumed
that matter in the "hot" universe during the early stages of its evolution consisted predominantly of an equal
number of nucleons and antinucleons which were annihilated during expansion [2]. It is possible that some
cosmic explosions now being observed were the result of annihilation. Little is known about this as yet, but
experience demonstrates that nature provides a wealth and variety of conditions and that it uses lavishly and
positively phenomena which man manages to observe with difficulty here on earth.
Annihilation Products. Any antiparticle can annihilate with the corresponding particle (opposite in sign
of charge). However, we focus our attention on the annihilation of pairs of stable particles and antiparticles,
i.e., of positrons and electrons and of antiprotons and protons. The lifetime of unstable particles is too short
Translated from Atomnaya Energiya, Vol. 44, No. 1, pp. 45-50, January, 1978.
40 0038-531X/78/4401-0040$07.50 O1978 Plenum Publishing Corporation
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Declassified and Approved For Release 2013/03/07: CIA-RDP10-02196R000700110001-5
10 20 50 100 400 MO Er,
MeV
101 0 ZOO 300 la 500
Quantum energy, MeV
Fig. 1, 'y-ray spectrum for annihilation of nucleon
pairs at low energy (in inset, a logarithmic energy
scale).
600 700
on an everyday scale. Of the unstable particles, only the annihilation of the antineutron, which has much in
common with the annihilation of the antiproton, has been observed thus far. The annihilation of antinucleons
and nucleons, which are the main carriers of the rest energy of matter, is most worthy of attention.
The annihilation of nucleon pairs (3 + p, etc.) occurs predominantly through the strong (nuclear) inter-
action. The effective annihilation cross section is about half the total interaction cross section over a very
broad energy range [3]. At low energy ( (H, 0=0.
(7)
Suppose that when t < 0 the reactor is in a steady state with a2(z, t