SOVIET ATOMIC ENERGY VOLUME 18, NUMBER 3

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• Document Creation Date: January 4, 2017
• Document Release Date: September 24, 2013
• Sequence Number: 3
• Publication Date: March 1, 1965
• Content Type: REPORT

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Volume 18, Number 8,
.Mareh,-1965
1
SOVIET
ATOMIC
ENERGY
ATOMHAFI 3HEPrI4F1
(ATOMNAYA iNERGIYA)
TRANSLATED FROM RUSSIAN
CONSULTANTS BUREAU
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REVIEWS OF PLASMA PHYSICS
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status of plasma theory, serving both as an introduction for students
'and for researchers entering the field, and as an authoritative, up-
to-date presentation of current knowledge for physicists prepared
by Soviet experts. Each volume contains a number of integrated
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STRUCTURE OF GLASS
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ATOMNAYA EN.ERGIYA
EDITORIAL BOARD
A. I. Alikhanov A. I. Leipunskii
A. A. Bochvar M. G. Meshcheryakov
N. A. Dollezhal' M. D. Millionshchikov
K. E. Erglis (Editor-in-Chief)
V. S. Fursov
I. N. Golovin
V. F. Kalinin
N. A. Kolokol'tsov
(Assistant Editor)
A. K. Krasin
I. F. Kvartskhava
A. V. Lebedinskii
I. I. Novikov
V. B. Shevchenko
A. P. Vinogradov
N. A. Vlasov
(Assistant Editor)
M. V. Yakutovich
A. P. Zefirov
SOVIET ATOMIC
ENERGY
A translation of ATOMNAYA ENERGIYA
A publication of the Academy of Sciences of the USSR
@ 1966 CONSULTANTS BUREAU ENTERPRISES, INC.
227 West 17th Street, New York, N. Y. 10011
Volume 18, Number 3
March, 1965
CONTENTS
PAGE
ENG.'
RUSS.
Report on the Award of the I. V. Kurchatov Gold Medal and Prize
253
201
The Microtron and Areas of its Application?S. P. Kapitsa
255
203
Accelerator with Nonlinear Helical Focusing?V. V. Vecheslavov and Yu. F. Orlov
262
209
Introduction of an Ion Beam into the Cyclotron?V. A. Gladyshev, L. N. Katsaurov,
A. N. Kuznetsov, L. P. Martynova, and E. M. Moroz
268
213
Quasiclassical Model of Ternary Fission?B. T. Geilikman and G. I. Khlebnikov
274
218
Concerning the Emission Times of y -Quanta as a Result of Fission?G. V. Val'skii,
D. M. Kaminker, G. A. Petrov, and L. A. Popeko
279
223
Application of the Yvon?Mertens Method for Solving Albedo Problems irt the Neutron
Diffusion Theory?Yu. N. Kazachenkov and V. V. Orlov
283
226
Use of the Method of Moments for Solving Equations of Neutron Thermalization in Infinite
Media?M. V. Fedulov
290
232
Electromagnetic Pumps for Alkali Metals?N. I. Marin, V. A. Povsten', T. V. Doktorova,
and E. M. Avilova
298
239
A Stainless Steel with High Capture Cross Section for Thermal Neutrons?I. S. Lupakov
and N. A. Vasil'ev
302
242
Distribution of Sr" in the Surface Level of Soils in the Soviet Union in 1959-1960
?V. I. Baranov, F. I. Pavlotskaya, G. A. Fedoceyev, g. B. Tyuryukanova,
L. M. Rodionova, E. V. Babicheva, L. N. Zatsepina, and T. A. Vostokova
305
246
ABSTRACTS OF DEPOSITED ARTICLES
Spatial and Energy Distribution of Scattered y-Radiation from a Unidirectional Source
in an Infinite Air Medium?S. M. Ermakov, V. G. Zolotukhin, V. I. Kukhtevich,
E. S. Matusevich, and B. A. Efimenko
311
251
Angular and Energy Distribution of Scattered y-Radiation Near an Isotropic Source
in an Infinite Air Medium?Yu. I. Kolevatov, V. I. Kukhtevich, E. S. Matusevich,
and 0. A. Trykov
313
252
Spatial Distribution of the Dose Rate of Air-Scattered Neutrons from a Unidirectional Point
, Source?S. F. Degtyarev and V. I. Kukhtevich
315
253
Certain Nonlinear Problems in Nuclear Reactor Theory?O. B. Moskalev and V. A. Chuyanov.
317
254
Effect of a Conducting Diaphragm on Plasma Equilibrium in Tokamak Devices
?V. D. Shafranov
318
255
Adiabatic Pinching of Hot-Ion Plasma (Description of the Device and the First Experiments)
?A. V. Bortnikov, N. N. Brevnov, V. G. Zhukovskii, and M. K. Romanovskii
320
256
Annual Subscription: $95
Single Issue: $30
Single Article: $15
All rights reserved. No article contained herein may be reproduced for any purpose what-
soever without permission of the publisher. Permission may be obtained from Consultants
Bureau Enterprises, Inc., 227 West 17th Street. New York City, United States of America.
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CONTENTS (continued)
Rules fOr Depositing (Storing) Articles
REVIEW OF THE GENEVA CONFERENCE
Investigations into the Problem of Controlled Thermonuclear Fusion?S. D. Fanchenko . . . .
Isotopes and Radiation?A. S. Shtan'
The Use of Isotopes and Radiation Sources in Hydrology and Hydrogeology?N. V. Churaev,
A. I. Yakovlev, M. P. VoloroviCh, N. Ya. Flekser, and S. Ya. Vartazarov
The Problem of Radioactive Waste Removal?A. N. Marei
LETTERS TO THE EDITOR
Determination of the Total Energy Lost by a Beam of Electrons as a Result of its Interaction
with a Plasma?A. K. Berezin, Ya. B. Fainberg, L. I. Bolotin, and G. P. Berezina. .
The Operation of the Cylinderizer in the Stellarator?B. I. Gavrilov, F. V. Karmanov,
and G. P. Maksimov
Experimental Verification of the Possibility of Using Stub Retarding Systems
in Accelerator Technology?P. I. Gos'kov
Total Interaction Cross Section of Neutrons with Benzene, Toluene and Sodium Acetate
in the Energy Range 0.03-0.5 eV ?I. S. Anisomov, V.1. Nikitin, A. I. Saukov,
and A. A. Ugodenko
Resonance Structure of the Cross Sections and its Influence on the Scattering Anisotropy
for Fast Neutrons and their Transmission in Iron?A. P. Suvorov, A. G. Guseinov,
and M. N. Nikolaev
Measuring the Moderation Length of Neutrons from a Po-Be Source in Graphite-Water
Lattices?Yu. M. Shalashov
Method of Investigating y-Radiation from the (n, y) Reaction on Separated Isotopes
?P. A. Rudak and E. I. Firsov
Dependence of the Counting Efficiency in Recording Fast Neutrons on the Geometry
of Plastic Scintillators?V. G. Zolotukhin and G. G. Doroshenko
Calculation of the Effective Resonance Integral for a Lump Consisting of a Mixture
of Nuclei of a Resonance Absorber and Continuous Cross-Section Absorber
?Yu. G. Pashkin and V. V. Chekunov
Presentation of the Reactor Dynamics Equations in Terms of the Reciprocal Period
?N. G. Chelintsev
Effebt of Pressure on the Heat Transfer in Nucleate Boiling of Liquid Metals
?V. M. Borishanskii and K. A. Zhokhov
Measurement of Radioactivity at the Surface of Aqueous Solutions?M. A. Belokurova,
N. E. Tsvetaeva, M. N. Kulichenko, and L. A. Ivanova
Investigation of Sorption of Radioiodine on Activated Charcoal, and Study of Forms
of Gaseous Iodine in Air?T. I. Smolkina and A. A. Chubakov
Radioactive Fallout on the Far-Eastern Shoreline of the Pacific Ocean in 1962-1963
?E. I. Markichev, A. D. Shramchenko, A. S. Lapardina, V. V. Peretti, E. I. Vasil'kov,
and V. V. Skornyakov
NEWS OF SCIENCE AND ENGINEERING
Physical Startup of the VK -50 Boiling Water Reactor at the Ul'yanovsk Nuclear Power
Station?A. Kubrochenko and V. Parfir'ev
Nuclear Instrumentation Discussed at Comecon?N. A. Shekhovtsov
Symposium on the Radiation Chemistry of Polymers?M. Kaplunov
Plasma Physics Seminar at Trieste
French Research Reactors and Power Reactors?V. A. Tsykanov
P A
ENG. I
G E
RUSS.
322
257
323
258 ?
327
?260
332
264
337
268
341
271
345
273
348
275
350
277
352
278
358
282
361
285
365
287
369
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292
377
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380
296
383
298
386
300
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302
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395
305
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CONTENTS (continued)
PAGE
ERG. I RUSS.
American Water Desalinization Specialists View Soviet Work
400
309
British Scientists Visit the USSR
401
309
Radioisotoce Advances in the Lithuanian SSR?S. Geciauskas and K. Valacka
402
310
The Russian date "Podpisano k pechati" of this issue was 3/3/1965 . This is equivalent to "approved
for printing." Publication did not occur prior to this date, but must be assumed to have taken place reasonably
soon thereafter.
Publisher
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REPORT ON THE AWARD OF THE
I. V. KURCHATOV GOLD MEDAL AND PRIZE
Translated from Atomnaya Lergiya, Vol. 18, No. 3,
pp. 201-202, March, 1965
311 PASOTb1 b onAcflot
SIAEPHOil 40134K
AKA/1E1%01R HAY
Anatolii Fedorovich
Dunaitsev
By decision of the Praesidium of the Academy of
Sciences of the USSR, the Igor' Vasil'evich Kurchatov
gold medal for 1965 was conferred upon Yu. D.
Prokoshkin, Doctor of Phys. Math. Sci., and the I. V.
Kurchatov Prize was awarded to A. F. Dunaitsev, V. I.
Petrukhin, Yu. D. Prokoshkin, V. I. Rykalin, for their
observation and investigation of the beta-decay of the
7r -meson (7r + + e+ + v). This research was con-
ducted with the aid of the 680-MeV synchrocyclotron
of the Joint Institute for Nuclear Research.
Valentin Ivanovich
Petrukhin
Yurii Dmitrievich
Prokoshkin
Vladimir Ivanovich
Rykalin
The special interest displayed by physicists in research on the beta-decay process of the pion is due to the pos-
sibility of directly verifying, by such a course of study, the validity of one of the main and general principles of the
universal theory of weak interactions: the hypothesis of the conservation of vector current in transitions with no
change in strangeness. This theoretical assertion put forth for the first time by the Soviet physicists Ya. B. Zel'dovich
and S. S Gershtein, and independently by the American physicists M. Gell-Mann and R. Feynman, extends to the
field of weak interactions, a fact quite familiar in electrodynamics, viz., that electrical charges on all the ele-
mentary particles are identical regardless of what interactions a particle participates in. The charges on the positron
and proton are identical in the strict sense, despite the fact that the proton takes part in strong interactions in addi-
tion, to electromagnetic interactions, while the positron does not.
This difference in behavior with respect to strong interactions means a difference in the magnetic moments of
these particles, but not in their charges.
The beta-decay process of the pion is singled out as a transition within the isotopic multiplet at zero spin,
from a large number of other weak interaction processes. Despite the fundamental nature of the pionic beta-decay,
this process had not been detected experimentally until very recently, because of the extremely low expected proba-
bility (about 10-8) and the consequent experimental difficulties.
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Scientific staff members of the Nuclear Problems Laboratory of the Joint Institute for Nuclear Research, viz.
A. F. Dunaitsev, V. I. Petrukhin, Yu. D. Prokoshkin, and V. I Rykalin, were the first in the world to find a solution
to this tricky problem ? they detected the beta-decay of the pion and carried out an experimental investigation of
the phenomenon.
In their preparation of the experiments, the authors designed a very elegant sophisticated high-speed electronic
system capable of recording rare cases of beta-decay of pions and separating them out from the thousand times more
frequent events of appearance of neutral pions via charge transfer between charged pions.
The basic components of this electronic system are a five-beam oscillograph with a resolution of 10-1-9 sec and
a multichannel coincidence circuit with 10-9 sec resolution. High-resolution total-absorption Cherenkov spectrom-
eters of high effectiveness and background insensitivity were designed to record the gammas emitted in the decay of
neutral pions. These instruments are the most highly advanced presently existing with such operating parameters.
The investigations were carried out since late 1961 on the synchrocyclotron of the Nuclear Problems Laboratory.
The beta-decay of the pion was discovered as a result of protracted measurements: 43 cases of this mode of decay
were recorded. All the characteristics of the observed phenomenon added to the evidence of the reliable identifica-
W(AL,F.e+e-H-v)
don made of this mode of decay alone. The total decay probability was w(n + 11++ v) = (1.1 ? 0.2) ? 10-8.
Both this value and the energy spectrum of pion-decay positrons are in excellent agreement with theoretical predic-
tion. The experimentally determined constant G characterizing the beta-decay intensity of the pion was found to
be G = (1.03 ? 0.11)G, where Ga is the vector constant of the neutron beta-decay process.
The experimental results obtained by researchers at CERN, Berkeley, and Columbia University, where studies
on the beta-decay of the pion were initiated somewhat later, are in accord with these findings.
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THE MICROTRON AND AREAS OF ITS APPLICATION
(UDC 621.384.611.3)
S P. Kapitsa
Translated from Atomnaya Finergiya, Vol. 18, No. 3,
pp. 203-209, March, 1965
Original article submitted June 15, 1964
The present article is a survey of the basic results obtained in investigating and developing a microtron
with a high-current beam. This new type of electron accelerator is compared with other medium-
energy electron accelerators. The areas of application of the microtron in various branches of science
and technology are briefly considered.
The development of modern accelerator technology follows two trends. On the one hand, accelerators with
ever higher energies, which make it possible to solve new problems in elementary particle physics, are being con-
structed while, on the other hand, an ever increasing importance is attached to lower-energy accelerators, which are
necessary for investigations in nuclear physics as well as for experiments connected with the use of high-energy par-
ticles in other areas of physics and technology. It is possible that accelerators have found the widest application in
those areas of science where the equipment and investigation methods developed in nuclear physics have been em-
ployed most widely. In particular, radiation chemistry has developed in this manner.
Electron accelerators which serve as sources of fast electrons and gamma bremsstrahlung gained the most wide-
spread use in these fields. Therefore, it would be of interest to consider the possibilities offered by the high-current
microtron, which constitutes a new efficient medium-energy electron accelerator.
The principle of the electron cyclotron was set forth in 1944 by Veksler in the first of his papers devoted to the
principle of phase stability [1]. Acceleration based on this method was first achieved in Canada [2]. However, this
and other similar experiments did not result in the construction ofan efficient accelerator, so that, until lately, the
inherent possibilities of the microtron were not recognized and realized. The question of widespread application of
this type of accelerator arose only after completion of the work performed at the S. I. Vavilov Institute of Physical
Problems, Academy of Sciences of the USSR, which led to the construction of an efficient high-current microtron.
Before considering the application of microtrons, we shall recall the main physical principles on which they
are based, and we shall briefly survey the results obtained in recent years at the Institute of Physical Problems and
other laboratories in the Soviet Union.
Operating Principle and Parameters of the Microtron
Electrons are accelerated in a microtron by a constant-frequency alternating electric field in a uniform and
steady magnetic field. In the vacuum chamber, the electrons move along circles which have a common tangent
point (Fig. 1). The accelerating resonator is mounted at this place. With each passage through the accelerating gap,
the electrons acquire a certain energy increment PE arid pass to the next circle (orbit). The synchronism of electron
motion and the variation of the superhigh-frequency field are a consequence of the fact that the duration of every
subsequent revolution is longer than the duration of the preceding revolution by the period T of the superhigh-frequen-
cy field. The revolution time t of a relativistic particle in the magnetic field H is proportional to its total energy E,
t
2:rtE
elic '
(1)
while the condition of synchronism in the microtron corresponds to the following relationship between PE and H and
the increment Pt of the revolution time:
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.610
Fig. 1. Schematic diagram of the microtron. 1) Cham-
ber; 2) magnet; 3) resonator; 4) waveguide; 5) ferrite; 6)
magnetron; 7) electron emitter; 8) high-vacuum pump;
9) extraction.
Fig. 2. Small microtron of the Institute of Physical Prob-
lems.
adequate, and the accelerator current and efficiency were
an efficient accelerator.
2\E1.
el/c = .
(2)
This relationship can be conveniently transformed into
the relationship
AEH
? =Q,?
Ho
(3)
where E0 = mc2 is the electron rest energy and Ho
= (27r ED /ecT) = (27r E0 /eX) is the cyclotron value of
the magnetic field for the wavelength X of the accele-
rating voltage. Microtrons, as well as linear accelera-
tors, usually operate in the 10-cm superhigh-frequency
range. At a frequency of 3000 Mc (X = 10 cm), the cy-
clotron field is equal to 1070 Oe. The fl parameter
constitutes the basic characteristic of the accelerating
conditions, and all the accelerator properties and its
limiting parameters are connected with this quantity.
Since S2 1, the particles are accelerated to an energy
of the order of the rest energy with each passage through
the resonator. Essentially, this constitutes the basic dif-
ference between a microtron and other accelerators of
relativistic particles with automatic phase control (syn-
chrotrons and phasotrons), where the energy increment
with each passage through the accelerating gap can be
small.
A consequence of the above property of micro-
trons is the fact that the strength of the electric ac-
celerating field is comparable to the strength of the
magnetic field. For electrons, E0 = 511 keV, and the
increase in their energy by such a value with each pas-
sage through the resonator constitutes the basic diffi-
culty in microtron design. This difficulty was solved
by using high-power generators of waves in the centi-
meter range, which were initially developed for radar.
It is obvious that, in its existing form, the microtron is
unsuitable for the acceleration of heavy particles, since
their rest energy is very high.
After N revolutions, the energy of the electrons
moving in the equilibrium phase will be equal to
E M2E0 E (4)
where Ei is the injection energy. Toroidal resonators
were used earlier in microtrons. The injection of elec-
trons was achieved as a result of their emission directly
from the walls of the flight gap, so that Ei = 0. The
imposition of the accelerating conditions on the par-
ticles was not controllable, the beam focusing was in-
low. Because of this, the microtron was not considered as
The improvements which resulted in the construction of
inducing particle into the acceleration process and the use of
256
a high-current microtron are based on new methods of
an efficient thermionic cathode for electron emission.
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Fig. 3. Large microtron of the Institute of Physical Problems.
Resonators consisting of square and round cavities, similar to one of the linear-accelerator resonators, are used. The
electron emitter is mounted on the outside flat wall of the resonator [3]. Electron emission occurs under the direct
action of the high-frequency electric field and is controlled by varying the cathode temperature. Thus, in contrast
to linear accelerators or betatrons, the microtron does not have an electron gun.
Several methods can be used for inducing electrons into the acceleration process. Under the so-called first
conditions of injection, the cathode is mounted at one half of the resonator radius. For the assigned geometry, the
injection conditions are satisfied in a wide range of il values, from 0.8 to 1.6, which allows smooth variation by a
factor of up to 2 for a fixed position and a constant number of orbits. This constitutes a new microtron characteristic,
which is of great practical importance, since it facilitates flexible control of the beam energy. Under the second
set of conditions, the cathode is located near the resonator axis, and the electrons pass through an additional opening
in the resonator wall. Under these conditions, electrons can be accelerated for l values ranging from 1.8 to 3 or
higher.
The resonator constitutes the most important unit of the accelerator. The resonators are usually demountable
and are made of oxygen-free copper, annealed and brazed in vacuum. The resonator's Q-factor is usually equal to
6000-10,000. By deforming one of its walls, the resonator frequency can be mechanically tuned to the frequency of
the superhigh-frequency oscillator. It is interesting to note that the operating strength of the magnetic field in the
resonator is close to the strength of the steady magnetic field; it attains 500-800 kV/cm. Experience shows that such
fields can be produced even in relatively poor vacuum (10-6-10-5 mm Hg), which is sufficient for the microtron's
operation. Lanthanum hexaboride (LaB6), which is characterized by high emission density, and great resistance and
stability, serves as the electron emitter. The shape and the position of the cathode, the resonator dimensions, and
also the efficiency of capture and the dynamics of electrons, are calculated by means of an electronic computer by
numerically integrating the equations of electron motion in the accelerator [4).
The spacing between the orbits (the orbit step) is virtually constant and is equal to about 3 cm for X = 10 cm.
Therefore, the extraction of particles from the accelerator does not involve difficulties; the electrons are extracted
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through an iron channel, which screens the field near the last orbit. The extraction efficiency is close to 90-100%.
As a result of phase stability, the electrons in the beam are bunched into blobs with a length of 145-1/20 A, which
follow each other at a distance equal to the wavelength A [5]. The energy spread is proportional to.0 and does not
depend on the number of orbits. For 0 = 1, SE = ?20 keV.
The magnetic field in the microtron is usually rendered uniform. The field strength in the chamber is equal
to 1000-2000 Oe and is maintained by the electromagnet, where the pole shape determines the required field uni-
formity. The magnetic field sends the particles back to the resonator, thereby accomplishing a peculiar 3600 focus-
ing. Essentially, the requirements for the field .uniformity are similar to the requirement for the rectilinearity of the ?
beam in linear accelerators. Nonuniformity of the field, especially in the direction perpendicular to the common
diameter of the orbits, leads to their drift and a loss of particles. The basic focusing of the beam is effected only by
the electromagnetic field of the resonators which, in contrast to the field in a linear accelerator, exerts a focusing
action on the electrons. The focusing strength depends on the shape of the through-flight openings. Thus, for instance,
in the case of oval openings and N = 10, the vertical dimension of the beam (along the magnetic field) is equal to
about 2 mm for a divergence of 1.5 ? 10-3 rad, while the horizontal dimension is 3-4 mm for a divergence of 1.5
? 10-2[6-8].
The high-frequency system of the microtron usually consists of a magnetron oscillator and a decoupling and
matching element (a ferrite or a load), which is located in the waveguide channel between the magnetron and the
resonator. The power necessary for the resonator's excitation is proportional to 02/1X and is equal to 250 kW for
= 10 cm and 0 = 1. The microtron efficiency, defined as the ratio of the power supplied to the resonator to the beam
power is presently equal to 30-35%.
The first 12-orbit high-current microtron [3] that was constructed in 1958 at the Institute of Physical Problems
has now been reconstructed. The new small microtron is shown in Fig. 2. The diameter of the poles is 750 mm,
while the magnet weighs 900 kg. 'At the 17th orbit, the electron energy attains 10 MeV for 0 = 1.2 and 18 MeV for
= 2. The mean beam power is 0.5 kW for a current of up to 50 mA in pulses with a duration of 2.5 psec and a re-
petition frequency of 400 cps. The accelerator's power consumption is equal to 15 kW. Figure 3 shows the general
view of the large microtron at theInstitute of Physical Problems. The pole diameter is 110 mm; the microtron is
calculated for 30-45 MeV [9]. At the present time, an energy of 25 MeV for a current of up to 20 mA in pulses was
obtained in this accelerator at the 28th orbit. A similar accelerator is presently being prepared for operation at
OIYaI for work in combination with a fast pulse reactor.
What are the maximum expected energies and currents in the microtron?
The maximum energy that can be secured in the microtron depends on the number of orbits and the parameter
0 in correspondence with expression (4). The maximum number of orbits is determined by the maximum allowable
nonuniformity of the magnetic field, which is inversely proportional to the square of the number of orbits [10]. Ac-
cording to the present state of magnetic technology, the maximum number of orbits is apparently equal to 50-100.
An obvious way to increase the energy is to use large SZ values. At this moment, resonators with 12 = 2 have been
calculated and constructed, and resonators with 0 = 3 or higher values have been calculated. Considering the switch
to large N and 12 values, a reasonable estimate of the maximum microtron energy would be 50-100 MeV.
The beam current is naturally connected with the power of ?the, superhigh-frequency source. The current is
physically limited by the interaction between the beam and the resonator and by .the coherent radiation of bunches
during their motion in the chamber [11]. Theoretical estimates of the maximum current yield values of 1-10 A (for
12 = 1); the maximum current value increases with an increase in SI . The above current values have not yet been
achieved experimentally; the maximum microtron current that has been obtained is equal to about 100 mA.
It should be mentioned that, at the present level of the technology of continuous generation of superhigh-fre-
quency oscillations, it is possible to produce continuous-operation microtrons with an energy of about 30 MeV and a
beam power measured in tens of kilowatts or more. The scale of such an accelerator would be comparable with that
of a standard cyclotron.
Comparison of the Microtron with Other Accelerators
It would be most interesting to compare the microtron with a linear electron accelerator, to which it bears the
greatest resemblance with respect to its essential properties. The basic difference between them is that a linear
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accelerator constitutes a machine consisting of many resonators connected in series and having a single common
beam, while the microtron can be considered as a device with parallel acceleration of many beams in a single reso-
nator and a correspondingly lower value of the characteristic impedance. However, in the case of a microtron, there
exists in practice a threshold power value (about 100 kW) beyond which electrons can be accelerated independently
of their final energy, which is determined only by the number of orbits and the magnet dimensions. In the case of
linear accelerators, regardless of the absence of such a lower limit, the power necessary for exciting a linear accele-
rator of reasonable length at comparable energies is much higher than the power required for exciting the single
resonator in a microtron. This results in the fact that a linear accelerator, in its present form, will always constitute
a pulse-action accelerator, barring an excessive increase in length or the use of cooled resonators, in particular,
superconducting resonators.
Linear accelerators provide the possibility of high-current acceleration of very short duration as a result of the
electromagnetic energy stored in them. In a microtron, due to the necessity of accelerating particles to strictly de-
fined values, such a possibility of operation under unsteady-state conditions does not exist.
In comparison with linear accelerators, the simplicity of the microtron constitutes its overwhelming advantage.
The microtron does not have an electron gun, which would require additional supply sources. The high-frequency
circuit and the resonator design are much simpler in the microtron. A microtron uses self-exciting nontunable mag-
netrons, which are characterized by great simplicity and efficiency in comparison with the high-power amplifying
klystrons used in linear accelerators.
Comparing the microtron to direct-action accelerators ? electrostatic and high-voltage rectifying devices ?
we see that virtually the same high monochromaticity of the beam can be achieved in the microtron. However, the
maximum microtron energy is much higher than the energy of direct-action accelerators. In the region of high ener-
gies (up to 5 meV), modern high-voltage rectifying devices have a considerable continuous power (up to 100 kW)
and high efficiency (50-80%). At the present time, they probably constitute the best high-power sources of fast par-
ticles in this energy range. However, the above advantages will be decisive only if the power of the device is con-
siderable. In the case of low power values, where energy losses play a secondary role, it is more convenient to use
microtrons or single-section linear accelerators, since the accelerator efficiency under these conditions is not so im-
portant, while the dimensions of the devices are smaller.
Betatrons and microtrons cover approximately the same energy range. However, the basic advantage of a
microtron in comparison with a betatron consists in its much higher intensity. Thus, at 12 MeV, the intensity of the
bremsstrahlung beam in the small microtron of the Institute of Physical Problems is equal to 3000 R/min. In con-
trast to the betatron, the electron beam can be extracted from the microtron without difficulties. The design of the
accelerator is very compact, while the energy efficiency of the microtron is much higher than that of a betatron.
Thus, in the range of medium energies (from 5 to 30-50 MeV), the microtron has presently many advantages
and new properties in comparison with other types of accelerators.
The physical principles of the operation of high-current microtrons have been thoroughly investigated, and the
basic technical problems connected with their design have been solved on the basis of the machines already con-
structed. In the next few years, this accelerator will undoubtedly be further developed, while the power of the ma-
chines and the energy will be raised. However, the possibilities of high-current microtrons can be clearly visualized
even now. Therefore, it would be of interest to discuss the new developments and fields of application that this ac-
celerator offers in science and technology [12].
Areas of Microtron Application
The high qualities of the microtron beam make it a promising injector for high-energy accelerators, such as
synchrotrons [13]. We should mention here the interesting experiments performed at the P. N. Lebedev Institute of
Physics, Academy of Sciences of the USSR, on the acceleration of positrons in a microtron [14]. As a result of in-
troducing an ingeneous conversion circuit and the subsequent acceleration of positrons, a record ratio ne+ine- = 1 to
2 ? 10-6 was obtained in this accelerator. It should be noted that the energy of accelerated positrons is equal to the
energy of initial electrons in this accelerator.
The progress in the field of experimental nuclear physics is connected with the development of the appropriate
investigation equipment. In the medium-energy range, the basic criterion for accelerators is the power. The
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precisely defined energy and the high intensity in a microtron offer new possibilities in nuclear physics, in particular
in studies of photonuclear reactions. The use of continuous-action microtrons is especially 'promising for the solution
of such problems. Progress in the field of these classical branches of nuclear physics is possible only if new experi-
mental equipment is provided and high-power accelerators are used.
The microtron can be an efficient source of fast neutrons as a result of the (y,n)-reaction. For the (y,n)-reac-
tion on heavy elements (U, Pb, W), the most advantageous energy is 25-30 MeV, while, for light elements (Be, D),
the energy should be -5_10 MeV. However, high-power linear electron accelerators are more suitable for these pur-
poses, since there are no stringent requirements for a monoenergetic beam in such cases. Due to the above-mentioned
possibility of operation under conditions of large currents with energy storage and pulse shortening, very large in-
stantaneous values of fast-neutron fluxes can be obtained by means of linear accelerators. On the other hand, the use
of small microtrons as neutron generators is very promising for purposes of radioactivation analysis. Thus, for in-
stance, the theoretical mean neutron flux produced by the small microtron of the Institute of Physical Problems is not
less than 1012 neutrons/sec. The use of microtrons-for analysis based on the determination of elements with respect
to their photonuclear reaction threshold is also promising. The accelerator's simplicity and the controllability of the
beam energy are the decisive factors in this case.
The efficient focusing in microtrons results in a small focusing point on the target, which offers great possibili-
ties for using the microtron in industrial 'flaw detection.
The production of electron and bremsstrahlung beams at energies of up to 20-40 MeV provides a basis for the
widespread application of microtrons in medical radiology for gamma-therapy and irradiation by fast electrons. The
accelerator's simplicity and reliability and the accurately defined beam energy are also of special importance in
this case. Therefore, the microtron now constitutes perhaps the best accelerator for medical purposes, since it has
advantages in comparison with betatrons, where the production of extracted electron beams is difficult, and with
linear accelerators, where the above energies cannot be achieved without using multisection accelerators, which are
characterized by complex and cumbersome superhigh-frequency supply. The use of efficient electron accelerators ?
microtrons ? is also advisable for beam disinfection and decontamination of-materials, food products, seeds, etc.
The wide field of -application of electron accelerators is related to problems of radiation chemistry and new
radiation methods for the treatment and modification of materials (metals, semiconductors, and polymers). In a
brief survey, it is impossible to give even a cursory outline of this field of accelerator application. We shall mention
only that, on the one hand, this field requires accelerators for laboratory and semi-industrial investigations; such ac-
celerators must have great flexibility and diversity of the parameters. On the other hand, many new production
methods, for instance the radiation vulcanization of tires, already urgently require-high-power sources of fast elec-
trons and bremsstrahlung and gamma radiation. In research as well as in industry, the high-current microtron offers
new possibilities in high-energy radiation techniques.
In this article we did not touch upon other fields of microtron application, in particular the fields of megavolt
electronics, relativistic plasma, and injection in accelerators. These fields form a part of modern physics and elec-
tronics, while the microtron essentially represents one of the results of developments in these fields. Our purpose
was to discuss the possibilities offered by the development of a new type of accelerator in other fields of science and
technology. The realization of these possibilities will depend to a large extent on how well the properties of the
microtron will be understood and the trends of its application in science and the national economy visualized.
LITERATURE CITED
1. V. I Veksler, DAN SSSR, 43, 346 (1944).
2. W. Henderson, H. LeCaine, and R. Montalbetti, Nature, 162, 699 (1948).
3. S. P. Kapitsa, V. P. Bykov, and V. N. Melekhin, ZhETF, 39, 997 (1960); 41, 376 (1961).
4. S. P Kapitsa et al., ZhETF, 41 (1961).
5. V. P. Bykov, ZhETF, 44, 576 (1963).
6. V. N. Melekhin, ZhtTF, 42, 622 (1962).
7. K. A. Belovintsev et al., Atomnaya energiya, 15, 62 (1963).
8. V. M. Melekhin, in; Transactions of the International Conference on Accelerators, Dubna, August 21-27,1963
(edited by A. A. Kolomenskii et al.) [in Russian] (Atomizdat, Moscow, 1964).
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9. S. P. Kapitsa et al., in: Transactions of the International Conference onAccelerators, Dubna, August 21-27,
1963 (edited by A. A. Kolomenskii et al.) [in Russian] (Atomizdat, Moscow, 1964), p. 1053.
10. V P. Bykov, ZhTF, 33, 337 (1963).
11. S. P. Kapitsa and L. A. Vainshtein, ZhETF, 42, 821 (1962).
12. S. P. Kapitsa, Vestnik AN SSSR, No. 10, 65 (1961).
13. K. A. Belovintsev et al., Atomnaya energiya, 14, 359 (1963).
14. K. A. Belovintsev and F. P. Denisov, Atomnaya eriergiya, 16, 253 (1964).
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ACCELERATOR WITH NONLINEAR HELICAL FOCUSING
(UDC 621.384.60)
V. V. Vecheslavov and Yu. F. Orlov
Translated from Atomnaya Lergiya, Vol. 18, No. 3,
pp. 209-213, March, 1965
Original article submitted March 19, 1964
The theory of an accelerator with nonlinear helical focusing is developed. The fundamental formu-
las are obtained for the example of cubic focusing. An approximate calculation of the region of sta-
bility, adiabatic attenuation, mechanism of transverse automatic phase stabilization, and effect of
perturbations is given. In quantitative characteristics, the accelerator is close to the strong-focusing
type.
A solution to the equations of motion of a charged particle in a nonlinear helical field (for the example of a
cubic field) was obtained in [1] without taking account of the many perturbing effects. The motion has the nature
of a superposition of comparatively large, nonlinear, coupled r-z oscillations, similar to a helical motion around a
circular orbit, and small nonlinear oscillations. The frequencies of the various oscillations are determined by the
amplitude of the nonlinear oscillations. In this sense there is no essential difference between spiral and sign-constant
[2] nonlinear focusings.
The effect of harmonic perturbations in nonlinear focusing essentially differs from the linear case by the de-
velopment of phase stability of the nonlinear oscillations [3,4].
In this paper we propose to use transverse phase stabilization in order to avoid passing through resonances dur-
ing acceleration. In contrast to sign-constant nonlinear focusing, conditions with a time-constant magnetic field
are here impossible; hence, passage through resonance is in no way justified. In the case considered, the ordinary
synchrotron condition, in which the field grows proportionally to the particle momentum, is possible. It is precisely
this condition (the only reasonable one in helical focusing) which is considered below.
A helical-focusing synchrotron may be set up, for example, in the form of deflecting magnets with a homo-
geneous field, alternating along the orbit, and short, nonlinear (six- or eight-pole) lenses set around the orbit with
rotational pitch / . It is assumed that the length / is much larger than the length of the magnets and lenses. The
fine structure of the field within the period (length of period equals / /3 and 1/4 for quadratic and cubic fields, re-
spectively) is a source of additional phase stabilization of the transverse oscillations, which is not considered here.
Below we shall operate with the mean quantities and (a kx /a r k), omitting the averaging sign. Regarding the
focusing as strong, we shall neglect the terms r/R.
Although the character of motion in nonlinear helical focusing differs substantially from the case of ordinary
linear focusing, the quantitative characteristics (phase volume, tolerances) are quite close for comparable param-
eters of these two cases. In this respect, the accelerator with helical nonlinear focusing has no advantage over ordi-
nary accelerators, but is of interest because of its characteristics for obtaining an accelerated beam.
Estimate of the Region of Stability
Here,
262
Without accounting for perturbations, the particle motion obeys the equation
Cr+ 2ictiP' ?a2V Y(P*3 O. (1)
a3//
= 6 dit3 111? '
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21t
.fp = (r+ iz) ?xi) ( ? iax) it-Eiv, a = ?1 '
where u, v are the axes of a coordinate system rotating in a helix, and x is the coordinate along the orbit.
The nonlinear helical part of the oscillations, according to [ii, is presented in the form of a Fourier series
(p(x)= a2h4.1 (v) exp [(?i)21' (2k + 1) (I + v) a?ri
with fundamental frequency v, which has the sense of the number of r-z oscillations in length /.
The co' efficients a 2k +1 (v) are found from the relations
I
= (14V2i(14V2+ 3v)2 ai 14
3y2 1 3 ( + 3v)2 (A + 5 v)2 ? ? ? )
? "13 ( 1+ 2'
a 4
'3 a2 (4 + 3v)2 3:02 (4 5 vr + ? ? ? )
3y3 ai124
a5 u6 (4+ 3v)4 (4+ 5v)2 ? ? ?
(2)
(3)
For v > 0 (particle motion in the direction of rotation of the lenses), series (2) converges for any values of v
From the re-
ly I 1, we must take account of
Eq. (5"), taking as the zeroth approximation b51, c, bn, cn instead of bu, cu, b31, c3i. However, carrying out the
calculation in this approximation, we obtain new values of p for v ; p of the order of 9v; -7v. This forces us
to consider the four equations following (5"), etc.
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Thus, for v all the terms of the series (4) are of the same order and series (4) diverges, starting from the
value of v for which the coefficients in front of bik and cik on the left-hand side of (5") become equal to the coeffi-
cient in Eq. (5').
These Considerations lead to the following rough estimate of the region of stability in the cubic field:
la12/1,-k
0>v > Yal 1.
The following notation is used in the above relationships:
C (z) = 2 (2 ? h) ? 24'6 (z),
h.- 1
ah(z)= (k ? 1) fq_j (z) ? h 13;,_,131- (z) ? a (z) (z).
1-1 t=o
If -a is everywhere substituted for a in (10) and (11), (8") will describe 6 -(r+, r_), while 6 -1(*)(r_- r+)
= 13-0(r_ - r+). The albedo of a cylindrical layer can be determined in a similar manner. In the zeroth approxima-
tion, all expressions for a spherical layer hold if a/2 (a= 1) is substituted for a in them.
Thermalization of Neutrons
The Yvon-Mertens method can be successfully used not only for solving single-velocity problems, but it can
also be applied to the problem of the reflection of thermal neutrons from media with an allowance for the change in
neutron energy (thermalization of neutrons).
Assume that neutrons fall on a half-space which does not absorb neutrons. We shall also assume that the
moderator nuclei are heavier, i.e., that their mass is much larger than the neutron mass. In each collision between
a neutron and a moderator nucleus, its energy (or the absolute velocity value) changes slightly. Davydov [6] showed
that this makes it possible to use the Fokker-Planck method, i.e., one can switch from the integral to a differential
expression in the kinetic equation. The velocity direction changes to a great extent in every collision; one cannot
switch to the differential expression in this case.
Since we are neglecting nonelastic collisions with nuclei of the medium, the expressions obtained hold only if
the mean neutron energy is lower than the first excitation levels of nuclei in the medium. Moreover, we shall con-
sider that the moderator nuclei are distributed as a free gas. Brockhouse and Hurst [7] have shown that this assump-
tion applies to the scattering of neutrons on the nuclei of a medium whose atomic weight is larger than the atomic
weight of aluminum. On the basis of all that has been said above, one can use the results obtained in [8]. The neu-
tron density is described by the equation
1 a a V
VV.AT 1 ' - - ? [V2A N - (1)2 A2N) V (A') ,
v2 av av 2 ?
-1
(12)
where A1 = (1// M)(mv2- 3kT), where m is the neutron mass, M is the mass of the moderator nucleus, / = 1/E is
the mean free path in the moderator, which is assumed to be constant, k is the Boltzmann constant, and T is the tem-
perature of the medium (OK).
We shall now switch to the new function No = N/v2. Instead of v, let us introduce the dimensionless velocity
v' =v(m/kT)-2", express E in kT units, and express the masses of the moderator nuclei in neutron mass units. Then,
expression (12) will assume the following form:
1 I , a2N0_Lv'
v'VN0? m11_1) av,2 + (2i/2-1)ON av? 4v'No [ No? yi dp,'"Vo (11')] =0.
?
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If E is substituted for the variable v'2 in (13), and x is expressed in 1 units, we obtain
tlaNO 2 [E ONO _LE LI_ aivo No] _f_ No dwN0 (11 0.
ax m aE2 ' aE 2
-1
(13 )
It was indicated in [9J that this equation holds for neutron energies satisfying the inequalities M >> 4kT/E and
E 0.
(109
Fig. 1. Spectrum of neutrons in a monatomic gas ?
with p = 1. The capture cross section obeys the 1/v
law. Solid line, calculation according to method of
moments; broken line, exact calculation.
294
Fig. 2. Spectrum of neutrons in a monatomic gas
with p = 20. The capture cross section obeys the1/v
law. Solid line, calculation according to method of
moments; broken line, exact calculation for p = co. _
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the flux of neutrons moving from the first to the second region, we use the approximate solution of Eq. (2), the qi
values will generally not correspond to the absorption of neutrons in the first region. Therefore, it is advisable first
to calculate qo by using the expression for the probability of absorption in the first region:
CO
go= 1 ? w (17) /V."'" (x)dx,
xo
and then to use Eqs. (6') for finding the qi/qo ratios. For the calculation of these ratios, one can apparently use the
?
coarsest approximation for N(1) ? its asymptotic form at infinity: N(1) 1/x2.
In order to estimate the applicability of the approximate solutions, we shall consider a medium consisting of a
monatomic gas with a scattering cross section independent of the relative velocity and with moderator atomic mass
values equal to 1 and 20. For p = 1, the approximate solution can be compared with the exact solution of the Wigner-
Wilkins equation while, for p = 20, it can be compared with the solution of the equation for a heavy gaseous modera-
tor [1]. The choice of a mass value equal to 20 is more or less arbitrary and is related to the fact that the calcula-
tion of the a ik coefficients for large p values is very cumbersome. On the other hand, p = 20 is sufficiently large
to use the solution of the equation for a heavy moderator for purposes of comparison.
In all calculations, N(1)(x) was used in the following form:
CO
g(1)(x)=--- const exp 2 r y (1) dt I
x [x+y (x)j ,) t it --Hy (t)i J '
where y(x) = w(x)/ Es, and g is the logarithmic energy decrement for a zero-temperature moderator. We used k-
degree polynomials as the expansion functions k(x); the qi values for p = 1 were calculated exactly, while, for p
= 20, the asymptotic form qi/qo was used in calculating g(1)(S(1) 1/x2). The error due to this is obviously negli-
gibly small; for p = 1 and p =.0 it is equal to zero. Actually, for p = 1, the qi values depend only on the total neu-
tron flux moving from the first to the second region and, therefore,
a
Fig. 3. Neutron spectrum and absorption density in a monatomic gas with p = 1. a) y(1) = 0.1; b) y(1)
= 0.3. Solid line, calculation based on the method of moments; broken line, exact calculation.
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TABLE 1. Values of the Mean Capture Probability
?y(1)
v av
exact
calc.
method of
moments
Maxwell
spectrum
0.1
0.3
0.1603
0.462
0.1596
0.458
0.1661
0.507
x,c)
y (pi (x) xdx
qi
xo
Po
(x)x (Ix
For p = 00 , due to the 6-like character of the G(x,x9 func-
tion, the qi values depend only on the 1I(1) value for x
= xo; consequently,
qi (Pi (xo)
qo q50 (x0) ?
Figures 1 and 2 show the N(x) curves, calculated by means of the exact and the approximate methods for two
values of the capture probability, which was assumed to be independent of the velocity (y/ g was equal to 0.1 and
0.3, respectively). Eleven terms of series (5) were used (n = 10), while xo was equal to 3. For convenience of graphic
representation, the neutron flux was assumed to be proportional to the capture probability at infinity. Approximate
calculation of the speCtrum for p = 20 yields a much worse result than for p = 1. This is entirely understandable,
since, in the first place, with an increase in the mass, the thermalization effect increases in the high-velocity region
and, in the second place, the functions G(x,x9 and Q(x) assume a peaklike form and series (9) converge very slowly.
However, for large p Values, the maximum deviation from the exact solution of Eq. (1) is connected not with the
fact that the solution of Eq. (1') is approximate, but with the substitution of G(x,x') for a'(x,x') which, in view of the
local character of the scattering kernel, leads to a considerable increase in density in the second region near x = xo.
We shall now consider the case of moderation where the capture probability depends on the energy. We shall
uSe a monatomic gas with p = 1 as the moderator while, for the absorber, we shall use SmI49 which, for Eo = 0.0976
eV, has resonance with r 0.064 eV [6]. We shall assume that the temperature of the medium is equal to 0.025 eV,
and we shall use a ratio of the absorber concentration to the moderator concentration for which y(1) is equal to 0.1
and 0.3 . We shall exclude from consideration the E > 0.4 eV region (the region where x > x1 = 4), thereby neglect-
ing the effect of thermalization on the spectrum for x > x1 in the x < x1 region. It should be mentioned that the
thermalization effect is also neglected in the xo < x < x1 region (as in the first example, xo = 3). However, the re-
sult of disregarding this is actually investigated in this article, while the x > x1 region is not considered at all.
Figure 3 shows the N(x) curves and the absorption densities y(x)N(x), calculated by means of the exact and the
approximate methods (for n = 10); Sm149 was used as the absorber. It is difficult to estimate the importance of dis-
crepancies between the curves calculated by means of the approximate and the exact methods. This problem must
be solved separately in each individual case. In practical applications, averaging of any function with respect to the
assigned spectrum is usually of the greatest interest. As an example, the table provides the values of the mean cap-
ture probability, reduced to the stattering cross section:
xi
v (x) N (x) dx
av -=
N (x) dx
The third cOlumn of the table proVicies the rthilts obtained by averaging y(x) with respect to the spectrum:
x2'
AX2 exp ? p for
N (x) =St
B 2 v (t) dt 1
x EY (x)- xi exp t [VM-i-t1 I
for x x*.
The limiting velocity x* and the A/B ratio were determined from the condition of the continuity of N(x) for
x = x* and the balance relationship, while 3, which is the ratio of the effective temperature of the neutron gas to
the moderator temperature, was obtained by using the Coveillot expression [7], which has the following form for p =1:
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(12)
The 0.92 coefficient was determined by analyzing the exact calculations for the case where the absorption cross sec-
tion obeys the 1/v law, i.e., for a constant capture probability. It is seen from the table that the mean probability
of Sm149 capture is much higher than the capture probability for x = 1; therefore, a lower value of the effective tem-
perature is obtained by using Eq. (12). However, it is clear that an increase in 13 will result in an even larger devia-
tion from the exact yav value, since the maximum of the spectrum will be shifted toward resonance. Thus, in com-
parison with the method of moments, less accurate results are obtained when the Maxwell spectrum is used for averag-
ing the capture probability.
In conclusion, the author hereby acknowledges his indebtedness to Yu. P. Pushkareva, who composed the pro-
gram for the electronic computer and performed the calculations.
LITERATURE CITED
1. E. Cohen, In: Transactions of the International Conference on the Peaceful Uses of Atomic Energy, Geneva,
1955 [in Russian] (Izd. AN SSSR, Moscow, 1958), Vol. 5, p. 487.
2. L. V. Kontorovich and V. I. Krylov, Approximate Methods of Higher Analysis [in Russian] (Fizmatgiz, Moscow-
Leningrad, 1962).
3. M. V. Kazarnovskii, A. V. Stepanov, and F. L. Shapiro, In: Transactions of the Second International Conference
on the Peaceful Uses of Atomic Energy. Reports by Soviet Scientists [in Russian] (Gosatomizdat, Moscow, 1959),
Vol. 1, p. 469.
4. M. V Kazarnovskii and F. L. Shapiro, Neutron Physics [in Russian] ?(Gosatomizdat, Moscow, 1961), p. 169.
5. S. I. Drozdov et al., In: Transactions of the Second International Conference on the Peaceful Uses of Atomic
Energy. Reports by Soviet Scientists [in Russian] (Gosatomizdat, Moscow, 1959), Vol. 1, p. 486.
6. J. Hughes and R. Schwartz, Atlas of Neutron Cross Sections. Second Edition [Russian translation] (Atomizdat,
Moscow, 1959), p. 316.
7. A. Weinberg and E. Wigner, Physical Theory of Nuclear Reactors [Russian translation] (IL, Moscow, 19,61).
297
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ELECTROMAGNETIC PUMPS FOR ALKALI METALS
(UDC 621.039.534.9)
N. I. Marin, V. A. Povsten', T. V. Doktorova, and E. M. Avilova
Translated from Atomnaya Energiya, Vol. 18, No. 3,
pp. 239-242, March, 1965
Original article submitted March 6, 1964
The development of a series of electromagnetic helical pumps rated at 0.1 to 150 m3/h for labora-
tory purposes is described together with their characteristics and constructional features.
The development of scientific investigations into molten-metal heat carriers requires the creation of reliable
and convenient pumps for carrying out experimental work on laboratory test systems. The following demands are
made of such pumps:. prolonged operation at heat-carrier temperatures 675-1075?K and higher, hermetic sealing (es-
pecially important in pumpting radioactive heat carriers), easy and smooth control of the delivery of liquid, minimum
over-all size.
At the present time, both mechanical and electromagnetic pumps are used for these purposes. The latter have
a number of positive qualities. They contain no moving parts, gaskets, or glands. They operate noiselessly and re-
quire little servicing. The relatively low efficiency of electromagnetic pumps is not of great significance for labora-
tory use.
Electromagnetic pumps, like electrical machines, are divided into dc and ac types.
The dc pumps are most promising for work at high temperatures and are distinguished by higher efficiency.
They are fed, however, from special dc sources at high currents and low output voltage (3000 to 20,000 A at 0.5 to 2
V), the creation of which presents great difficulty.
Single-phase ac pumps are very simple, and have therefore enjoyed wide popularity. A serious failing of this
type of pump is the comparatively short life of the working parts (500 to 1000 h), which limits their use.
0 330
ENIV-1
298
0 330
ENIV -2
0 385
0 500
1.1
ENIV-3
0 500
ENIV -4
ENIV -5
Fig. 1. Dimensions of helical electromagnetic pumps.
0 61 5
ENIV -6
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TABLE 1. Main Characteristics of the Series of Helical
Electromagnetic Pumps
Characteristics
Type of pump
th4,...,
z
th; cq
3
,...., co
si
,..: ?t?
Z
31

s6
Delivery, m3/h
0.4
2
10
50
85
150
Pressure ? 10-5
4.7
2.5
6
5
4.5
6
N / m2
Heat carrier
K
NaK
NaK
NaK _
NaK
NaK
Operating temp.,
725
875
675
675
675
775
?K
Power kVA
3.7
7
33
59
140
170
Weight, kg
100
120
400
550
650
1200
Suitable three-phase ac pumps for laboratory use
include those of the helical type, distinguished by com-
pactness and giving high pressures. These pumps are fed
directly from a three-phase ac network, and make it pos-
sible to change the direction of pressure of the molten
metal by reversing the phases of the stator winding. More-
over, they permit a supply of one of the main parts of
the pump (the stator) to be made available by, electrical
machinery factories in conjunction with serially produced
electric motors. For this reason, from the very beginning,
preference was given to pumps of the helical type in the
Physical Power Institute of the State Committee for the
Use of Atomic Energy, USSR.
It was necessary to develop a pump for transporting
NaK alloy at 10 m3/h at a pressure of 6 ' 10-5 N/m2.
This pump may be used for a large number of test sys-
tems. The temperature of the heat carrier at the first
stage did not exceed 675?K.
Subsequently, a series of helical electromagnetic
pumps with nominal deliveries of 0.5, 2, 10, 50, 85, and
150 m3/h and nominal pressures 2.5 to 6 ? 10-5 N/m2
was developed on the basis of tests made in the manu-
facture, improvement, and service of this pump. Depend-
ing on the rating and physical properties of the metal be-
ing pumped, the efficiencies of these pumps varied from
5 to 25%. The table and Fig. 1 indicate the main charac-
teristics of the series of pumps developed.
The same constructional arrangement was taken
for the whole series of helical electromagnetic pumps,
the pump being disposed vertically, ensuring convenient
discharge of the molten metal. From considerations of
compactness, axial in- and outflow of the metal was
chosen.
The construction of the 10 m3/h electromagnetic
pump is shown in Fig. 2, and its general view in Fig. 3.
The pump consists of the body 6, the stator 2 (the three-
phase winding of which creates the rotating magnetic
field), the internal core 3 (serving to complete the cir-
cuit of the magnetic flux), the working part 1, and the
input and output guiding cones 4.
The stator core is composed of electrotechnical
steel sheet. The sheets are pressed into the body, and
the whole packet held by spring rings placed in grooves
Fig. 2. Schematic arrangement of a 10 m3/h helical in the body on both sides of the packet. To ensure pre-
electromagnetic pump. cise assembly and prevent slipping of the packet, a longi-
tudinal key is arranged in a groove of the body and
packet. A three-phase winding is set in channels in the stator. The whole electrical insulation of the stator is made
on a silicon-organic basis.
In order to reduce heat losses and ensure normal working conditions of the winding, a heat-insulating air gap
lies between the working part and the stator. In addition, heat is carried away from the winding by water-cooling.
Since the outflow of heat from the end part of the windings is harder than from the central region, between the work-
ing part and the end windings are placed wedge-shaped copper sleeves 5 capable of being cooled.
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Fig. 3. General view of a 10 m3/h electro-
magnetic pump.
4 6 8 TO 1? /4
Delivery, m3/h
The inner core is made of electrotechnical steel plates laid
on the tube of the lower guiding cone.
A shaped flange is slid on to the free end of the tube, and on
this freely sits the upper guiding cone. The upper and lower guid-
ing cones are of similar construction, with "blades" welded onto
them along a helical line. The slope of the helical line varies be-
tween 9 and 900. The guiding cones are intended to produce a
smooth change in the velocity and direction of motion of the heat
carrier on entering and leaving the pump. Rings 7, set on the intern-
al core, play the same part as the short-circuiting rings in the asyn-
chronous electric motor. The working part is made in the form of
a stainless steel tube, on the inside of which is cut a helical spiral,
transforming the rotational movement of the liquid into forward
motion. Apart from this, the spiral strengthens the working part. A
stainless steel shell serves as inner wall of the working part; this
houses the packet of plates of the inner core. The thermal expan-
sion of the working part is compensated by means of the external
tubing, for which a suitable compensation system must be provided.
The stator and internal core are set up on a thrust flange
which ensures coaxial alignment.
Up to the present, pumps with 0.4 to 85 m3/h deliveries have
been made and tested. During the testing, certain difficulties as-
sociated with the electrical insulation of the plates in the internal
core were overcome. The electrical insulation of the plates must
operate at a temperature of 675 to 775?K. Initially the plates were
insulated with liquid glass with an admixture of alundum or a high-
temperature silicon-organic protective coating. In these cases, how-
ever, the evolution of gases and vapor from the insulation on heat-
ing led to an increase in pressure in the internal space of the core,
as a result of which the walls of the working part deformed and the
internal hydraulic resistance of the pump increased considerably.
For this reason the insulation in question was replaced by the oxide
type. The pumps had stable characteristics, in satisfactory agree-
ment with calculated values.
Pumps with a nominal delivery of 10 m3/h have been used
Fig. 4. Experimental characteristics of a 10 for longer periods. On the whole they have been operated on the
m3/h helical electromagnetic pump. test bed for more than 50,000 h. One such pump operated more
than 20,000 h with NaK alloy at a mean temperature of 530?K and
continued to work successfully. For some tens of hours it worked at an alloy temperature of 670?K with brief rises to
700 or 750?K. During service there was no case of the system ceasing to work on account of the pump going out of
order. The pump worked stably, noiselessly, and with a minimum demand for servicing. At the present time two
such pumps are operating satisfactorily in the radioactive loop circuit of the BR-5 reactor with NaK alloy. The dura-
tion of service of the pimps in this circuit is more than 10,000 h at a mean temperature of 625?K in the alloy. For
some tens of hours the pumps operated at alloy temperatures 725-775?K. Figure 4 shows the experimental charac-
teristics of these pumps.
A pump rate at 0.4 m3/h has so far operated for more than 500 h, pumping molten potassium at 525 to 575?K.
For 10 h it operated at metal temperature 815?K and for 1 h at 900?K. Meanwhile, the temperature of the winding
did not rise above 365?K, which indicates the possibility of using such pumps to pump molten potassium at tempera-
tures above 875?K. The end sections of this pump were preliminarily heated by auxiliary nichrome heaters in ceram-
ic beads, and the central part of the pump tract was heated by the thermal power losses in the walls of the working
part.
300
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The 50 m3/h pump has so far worked more than 2000 h at a metal temperature of 525 to 625?K and is ready
for tests.
In using a 150 m3/h pump one must bear in mind the fact that the height of the channel in the working parts
of the electromagnetic pumps in the series developed is relatively small (2 to 10.5 mm). Hence, in some cases
where the liquid metal is insufficiently pure, there may be blocking of the channel.
The individual pumps of the series were calculated for pumping a definite heat carrier. They may, however,
also be used for pumping other alkali metals, but in so doing one must take account of the electrical conductivity of
the molten metal and the stability of the material in the working part. For a higher electrical conductivity of the
metal, the supply voltage must be correspondingly lowered, since otherwise the pump may develop an impermissibly
high pressure for a low delivery.
Thus, in the course of development, we have been able to design a convenient and reliable construction of
electromagnetic helical pumps for pumping liquid alkali metals at a temperature of 675 to 725?K. The pumps have
small over-all size, are easily and smoothly regulated by adjusting the supply voltage, and may be coupled directly
to the electrical network.
At the present time work is continuing on perfecting the construction of the pumps and measures are being
taken to raise the maximum temperature of the metal pumped (to 825 or 875?K and higher).
In conclusion, the authors thank N. M. Turchin for help in testing the pumps. They also thank Chief Engineer
of the "Dynamo" Works, I. L. Litvak, and the factory staff who took part in preparing the stators.
301
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A STAINLESS STEEL WITH HIGH CAPTURE CROSS SECTION
FOR THERMAL NEUTRONS
(UDC 621.039.546/669.15)
I. S. Lupakov and N. A. Vasil'ev
Translated from Atomnaya Energiya, Vol. 18, No. 3,
pp. 242-245, March, 1965
Original article submitted March 11, 1964
Data are given on the technological and mechanical characteristics of a new stainless steel of the
austenite class, mark EP-229 (Kh17G21N15T), with a relatively high capture cross section for therm-
al neutrons. The authors describe its stability to general and intercrystallite corrosion in water plus
steam and its structural stability under prolonged exposure to high temperatures. This steel can be
used instead of nickel or Kh18N1OT steel in certain parts of nuclear reactors.
Steel EP-229 (Kh17G21N15T), which has relatively high capture cross section for thermal neutrons, was de-
veloped for use in certain parts of nuclear reactors instead of nickel and steel Kh18N10T, which are not altogether
satisfactory. Nickel has a relatively high capture cross section (0.42 cm-1), but it is scarce and hard to work. Steel
Kh18N1OT fails on account of its inadequate capture cross section (0.25 cm-1). Steel EP-229 is relatively cheap and
workable, and has a macroscopic capture cross section for thermal neutrons of 0.46 cm-1 ? higher than for stainless
steel, Nimonic or nickel. The high cross section is achieved by adding a large amount of manganese, which has a
capture cross section 2.5 times higher than nickel. Manganese also has a short half-life of induced radioactivity [1].
The neutron-physics and other properties of EP-229 thus make it suitable in certain cases for replacing pure nickel
or Khl8N10T.
An important property of any material is its workability, i.e., the ease with which it can be rough-fabricated
and processed by hot and cold deformation, welded, machined, etc. The workability of EP-229 under hot and cold
plastic deformation was confirmed during the preparation of high-grade electropolished tubes of 17.0 x 1.5 mm
diameter. The tubes were prepared both from centrifugally cast and from forged blanks with the following certified
composition (wt./0): C s 0.1; Si s 0.8; Mn = 20.0-22.0; Cr = 16.0-18.0; Ni = 14.0-16.0; Ti = 0.35-0.70; S 0.03;
P Is 0.045.
In investigating the steel's structure with the aim of choosing the optimum composition, it was found that add-
ing 0.5% or more Ti causes the formation of a new phase,, whose quantity increases with the Ti content. In its ap-
pearance and in its distribution among the austenite which forms the main structural constituent, this new phase some-
what resembles the a-phase. However, x-ray analysis showed that it is really a x -phase, 'with microhardness twice
as great as that -of the austenite.
As the 'steel was intended for welded structures, it was necessary to test its weidability. The difficulty here
was the presence of the manganese.. The effect of manganese on the weldability of austenitic steel is known to de-
TABLE 1. Weldability of Steel EP-229
Mark of
welded steel
Mark of
welding rod
Cracks
present '
EP-229 + 4-229
'EP-229 + EP-229
EP-229 +10118GIOT
EP-229 + KW:81\11'0T !
P-229t
Sv -.04KMON11 M3
EP-229
Sv-04Kh19N11M3
None
None
N-one
None
302
pend .on the composition of the welded seam [.2]. In two-
phase .austenite?ferrite seams of steel 18-8, increase in the
manganese content (which causes the appearance of a whol-
ly austenitic structure in the seam metal) can lead to the
appearance of heat cracks. Howev-er, if the introduction .of
5-7% Mn in the seam structure does :not eliminate the fer-
rite component, the deleterious effect of manganese does
not ,appear. Welded seams of steel 25-20 (of purely ,a,usten-
itic -structure) become more resistant to heat cracks on ad-
ditional alloying with manganese [2J. Favorable effects of
manganese on weldability are ,also noted in [3].
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TABLE 2. Tension Testing of Initial Welded Specimens
Mark of
welded steel
Mark of
welding rod
Strength,
kg/ mm'
Point of
failure
EP-229 + EP-229
EA-400/10
55.3
Main
metal,
seam
EP-229 + EP-229
EP-229
54.8
Main
metal
EP-229 + EP-229
(tubes)
Sv-04Kh19N11M3
54.7
Same
EP-229 + EP-229
(tubes)
EP-229
52.5
Same
EP-229 + EP-229
No welding rod
49.7
Seam
TABLE 3. Tension Testing of Welded Specimens after
Annealing at 350?C
Mark of
welding rod
Annealing
time, h
Strength,
kg/mm2
Point
of failure
EP-229
500
54.9
Seam
EP-229
1500
56.6
Seam
Lei -400 /10
500
56.8
Main
metal
EA-400 10
1500
58.0
Main
metal
TABLE 4. Impact Bending Tests of Welded Specimens
Mark ofImpact
welding rod
Aging time, h
strength,
kg /cm 2
Notch
location
EP-229
Initial state
11.0
Seam
EP-229
500
8.0
Seam
EP-229
1500
8.6
Seam
EP-229
Initial state
8.3
Fusion
.
zone
EP-229
500
7.6
Same
EP-229
1500
11.2
Same
EA-400/10
Initial state
8.5
Same
EA-400/10
-500
7.2
Same
EA-400/10
1500
7.8
Same
6032-58, without heating. It was found that 17 x
EA-400/10, and SvO4Kh19N11N3 or without rods,
Steel EP-229 contains 20-22% manganese: there
is no information on the effect of such a quantity on
the weldability of this type of steel. T-shaped speci-
mens were used to investigate the tendency of welded
seams to form heat cracks during welding. The speci-
mens were welded with a "noodle" of the base metal,
wires of Sv-04Kh19N11M3 and EA-400/10 electrodes.
They were then examined for cracks. The welds were
broken on the press and again examined: the results
are shown in Table 1.
It was found that steel EP-229 does not tend to
form heat cracks on welding.
To estimate the strength and adhesiveness of
the welded joints, we made butt joints of 6- to 10-mm
thick strips and tubes 17 x 1.5 mm in diameter. Spe-
cimens were then prepared for testing by tension, flex-
ing, and impact bending. Those for impact bending
were 5 x 10 x 55 mm, while the cross sections of the
working part of the specimens for tension and flexing
were 5 x 15 mm and 4 x 10 mm, respectively. The
tests were made in accordance with GOST 6996-54.
The specimens were tested either directly after weld-
ing (Table 2) or after retention at 350?C for 500 or
1500 h (Table 3). It is seen that rod welding gives
fairly strong seams initially. For rodless welding, the
strength of the seams on the 17 x 1.5 mm tubes was
somewhat reduced.
Increasing the retention time at 350?C is found
to cause some strength increase in the welded speci-
mens, evidently due to aging.
Table 4 shows test results for welded specimens
under impact bending, either immediately after weld-
ing or after annealing for 500 or 1500 h at 350?C. It
is found that the weld seams and fusion zones have
fairly high impact strength, which is not much affected
by the annealing.
Specimens welded with EP-229 or EA-400/10
welding rods withstood bending through 180?C.
The welded specimens were tested for intercrys-
tallite corrosion resistance by the AM method of GOST
1.5-mm tubes of fourth-melt EP-229, welded with rods of EP-229,
did not undergo intercrystallite corrosion.
EP-229 can be satisfactorily arc-welded, argon-arc welded, and contact seam welded. Welded joints between
this steel and OKh18N1OT did not tend to form heat cracks. The seam was of high strength for all types of welding.
For arc welding, we recommend L-400/10 electrodes, and for argon-arc welding we recommend the use of welding
rods of the main metal and Sv-04Kh19N11M3 wire.
The strength and ductility of the steel were determined by tension testing of fivefold specimens of 6-mm diam-
eter at 20, 350, and 500?C. The impact strength was measured at room temperature on austenitized Menage speci-
mens at 1050?C. The results (Table 5) show that P-229 has fairly good mechanical characteristics both at room tem-
perature and at 350 and 500?C, i.e., its strength properties are comparable with those of OKh18N10T.
303
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TABLE 5. Mechanical Properties of Steel at Room and
High Temperatures
Test
temp.,
?C
?B'
2
kg/mm
0 0, . 2
kg/mm2
%
ctR,
kg ? m/ cm2
20
350
500
58.7
47.0
44.9
25.0
19.2
17.3
36.3
29.5
26.4
53.7
47.3
46.7
10.2
?
?
TABLE 6. Corrosion Tests at 350?C and 170 atm
Oxygen content
of water,
mg/liter
Test
duration,
h
Corrosion
rate,
g(m2. day)
GOST 5272-50
scale mark
0.025
50
300
500
1000
0.22
0.026
0.004
0.003
2
1
0
0
1
50
0.29
3
To test the degree of embrittlement caused by
high working temperatures, we studied the effect on the
mechanical properties and structure caused by prolonged
heating. For this purpose, the austenitized impact speci-
mens were heated at 350? for 500, 1000, and 4000 h. Dur-
ing this time, the impact toughness and hardness were
determined and the microstructure examined. The im-
pact toughness and hardness did not change appreciably
after 4000 h, i.e., the steel was not embrittled and re-
tained its toughness. Metallographic investigations of
these specimens showed that after austenitization from
1050?C the steel acquires the austenite structure with a
small amount of the x -phase. No appreciable change
was found after keeping at 350?C for 4000 h, which
showed the structure to be adequately stable.
To test the corrosion resistance and suitability for
use in wet steam at high temperatures, we investigated
the general corrosion in water at 350?C and 170 atm.
Austenitized specimens were tested in water containing
0.06 mg/liter chloride ion and 0.025 mg/liter oxygen,
and also in water containing up to 1 mg/liter oxygen.
The test durations were 50, 300, 500, and 1000 h.
From Table 6 it is seen that the corrosion rate in de-aerated water (15_0.025 mg/liter 02) decreases with in-
crease of test duration; increasing the 02 content to 1 mg/liter does not appreciably increase the corrosion rate.
EP-229 is thus a very corrosion-resistant steel.
We have thus developed a steel, EP-229 (Kh17G21N15T) with macroscopic capture cross section for thermal
neutrons of 0.46 cm-1, possessing adequate mechanical and corrosion properties. It has high structural stability under
prolonged heating at 350?C and is scarcely embrittled. It can be satisfactorily arc-welded, argon-arc welded, or
contact seam welded. Its workability is adequate for the production of tubes, plates, and moldings. It can be used
as a material for absorbing thermal neutrons, replacing steel Kh18N10T, nimonic, or technically pure nickel.
LITERATURE CITED
1. B. Price, K. Horton, and K. Spinney, International series of monographs on nuclear energy: Radiation shielding.
Pergamon Press (1957).
2. B. I. Medovar, Welding of Chrome?Nickel Austenitic Steels (Mashgiz, Moscow, 1958).
3. H. Weigand, Schweissen und Schneiden, 10, 2 (1958).
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ft
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DISTRIBUTION OF Sr9? IN THE SURFACE LEVEL OF SOILS
IN THE SOVIET UNION IN 1959-1960
(UDC 551.577.7)
V. I. Baranov, F. I. Pavlotskaya, G. A. Fedoceyev,
E. B. Tyuryukanova, L. M. Rodionova, E. V. Babicheva,
L. N. Zatsepina, and T. A. Vostokoval
Translated from Atomnaya Energiya, Vol. 18, No. 3,
pp. 246-250, March, 1965
Original article submitted February 6, 1964; after revision May 13, 1964
Data are presented on the distribution of Sr" throughout the territories of the Soviet Union in 1959-
1960. The distribution is observed to be of a latitudinal nature with maximum values within the
limits 50-30?N. On the average, the Sr" content in the surface level of soil coverage with a thick-
ness of up to 5 and 15 cm amounted to 14.1 and 17.8 mCi/km2. respectively. The absence of any
increase in content of this isotope in 1960 as compared with 1959 indicates that during the period
investigated the quantity of Sr" deposited from the atmosphere onto the earth's surface .corresponded
to the quantity which, because of various processes, was removed from the upper layer with a thick-
ness up to 5 cm.
In studying the ways of assimilating radioactive products from nuclear explosions into the human organism, it
is essential to know the content of the various radioactive isotopes in all links of the food chain, commencing with
the soil and the vegetation covering. This is due to the fact that as a result of deposition from the atmosphere the
radioactive isotopes are retained directly in the above-ground part of the plant or are concentrated in the upper layer
of the soil, whence they enter the plant through the root system.
There is available, at present, a great deal of information concerning the determination of the S190 content ?
one of the most dangerous radioactive isotopes to the health of mankind ? in the upper layer of the soil coverage of
a number of countries [1-3]. The aim of the present paper is to produce similar data for the Soviet Union.
Samples were collected in June-July 1959 and July-September 1960 on level, open virgin land sections by
means of special frames with an area of 25 x 20 cm and depths of 0-5 cm (at certain points with layers up to 5, 5-10,
and 10-15 cm). The sampling points were selected on the basis of a preliminary radiometric survey with the usual
13 -y-radiometers over a grid 5 x 10 m; the necessity for this arose because the Sr" content of samples of the soil ?
vegetation coverage collected at relatively small distances from one another may differ by more than a factor of
two. This can be seen from the data of Table 1 (here, and henceforth, the mean arithmetical values of two parallel
determinations are given).
The Sr" contents were determined by a radiochemical method after leaching with 6 N HC1 [4]2
A correction for the contribution to the chemical yield of the carrier by stable strontium, contained to a con-
centration of more than 30 mg/kg in the samples was introduced. The analytical error (a /x- ? 100%, where a is the
mean-square error; is the arithmetic mean value) for samples with a radioactivity dpm was _?10/0 and with a
radioactivity of 1.5
MeV
/
Experimental
Calculated
1
2
3
, 4
5
6
G'sf 1>

7
asf 1
8
/ / ?F-3f i \
9
/ Gsf 1 \
/ (Y41 \
/ _cr_.\