SOVIET ATOMIC ENERGY VOL. 57, NO. 4

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• Document Creation Date: January 4, 2017
• Document Release Date: February 22, 2013
• Sequence Number: 4
• Publication Date: October 1, 1984
• Content Type: REPORT

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April, ,1985"
ISSN 0038-531X
Russian Original Vol. 57, No. 4; October, 1984
SATEAZ ?57(4)-673-750 (1984)
i - ,
SOVIET
ATOMIC
ENERGY
ATOMHAH 3HEPENA
CONSULTANTS-BUREAU, NEW YORK
TRANSLATED FROM RUSSIAN
-(ATOMNAYA ENERGIYA)
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SOVIET
ATOMIC
ENERGY
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Editor: 0. D.. Kazachkovskii
Associate Editors: A. I. Artemov, N. N. Ponomarev-Stepnoi,
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E. V. Kulov E. I. Vorob'ev
B. N. Laskorin V. F. Zelenskii
V. V.~Matveev ,
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SUVILI ? A I UMIV LNLKbY
A translation of Atomnaya Energiya
April, 1985
Volume 57, Number 4 October, 1984
CONTENTS
Engl./Russ.
ARTICLES
Power Startup of the IBR-2 Reactor and the First Physics Investigations
in Its Beams - V. D. Anan'ev, V. A. Arkhipov, A. I. Babaev,
Yu. M. Bulkin, B. N. Bunin, V. S. Dmitriev, N. A. Dollezhal',
L. V. Edunov, A. D. Zhirnov, V. L. Lomidze, V. I. Dushchikov, _
Yu. I. Mityaev, Yu. M. Ostanevich, Yu. N. Pepelyshev,
V. S. Smirnov, I. M. Frank, N. A. Khryastov, Yu. M. Cherkashov,
E. P. Shabalin, and Yu. S. Yazvitskii. . .
Nuclear Data Requirements. for. Fast Reactors - V. N. Manokhin
and L. N. Usachev. . . . . . . . . . . . . . . . . . . . . . . .
Measurement of the Fission Cross Section of the 235U Isomer by Thermal
Neutrons - V. I. Mostovoi and G. I. Ustroev. . . . . . . .. . . . .
Comparative Analysis of Estimates of Neutron Radiative Capture Cross
Sections for the Most Important Fission Products
- T. S. Belanova, L. V. Gorbacheva, 0. T. Grudzevich,
A. V. Ignatyuk, G. N. Manturov, and V. I. Plyaskin . . . . . . . .
Absolute Measurements of the 239Pu Fission Cross Section for .
8.5-MeV Neutrons - R. Arlt, H. Bohn, W. Wagner, M. Dosch,.
G. Musiol, H.-G. Ortlepp, G. Pausch, K. Herbach (GDR),
I. D. Alkhazov, E. A. Lanza, L. V. Drapchinskii, V. N. Dushin,
S. S. Kovalenko, 0. I. Kostochkin, V. N. Kuz'min,
K. A. Petrzhak, B. V. Rumyantsev, S. M. Solov'ev,
P. S. Soloshenkov, A. V. Fomichev, and V. I. Shpakov (USSR). . . .
Measurement of the a Value at 235U Resonances.
-Yu. V. Adamchuk, M. A. Voskanyan, G. V. Muradyan,
P. Yu. Simonov, and Yu. G. Shchepkin . . . . . . . . . . . . . . .
Experimental Investigation of the Form of the Energy Distribution of
Neutrons in the Spontaneous Fission of 252Cf - M. V. Blinov,
G. S. Boikov, and B. A. Vitenko . . . . . . . . . . . . . . . . . .
Effects of the Fluctuation of the Resonance Parameters in the Average
Neutron Cross Sections - N. Koyumdzhieva, S. Toshkov,
and N. Yaneva. . . . . . . . . . . . . . . . . . ? . . . ?.
Total Neutron Cross Sections of Radioactive 153Cd and Stable 152Gd
- V. P. Vertebnyi, P. N. Vorona, A. I. Kal'chenko,
V. G. Krivenko, and V. Yu. Chervyakov . . . . . . . . . . . . . . .
Cross Sections of the Interaction of Fast Neutrons with Chromium and
Its Isotopes - I. A. Korzh, V. A. Mishchenko, M. V. Pasechnik,
and N. M. Pravdivyi. . . ? . . . . . . . . . . . . . . .
Spectrum of Secondary Neutrons and Cross Section of the (n, 2n)
Reaction at Niobium - A. A. Lychagin, V. A. Vinogradov,.
0. T. Grudzevich, B. V. Devkin, G. V. Kotel'nikova,
V. I. Plyaskin, and 0. A. Sal'nikov. . . . . . . . . . .
673
227
.
683.
234
.
692
241
.
694
243
.
702
249
.
705
251
.
714
257
.
716
259
.
718
260
.
. 721
262
726
266
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VY w U- ^ i^
(continued)
Engl./Russ.
Neutron Generator with Yield of 1012 sec-' - G. G. Voronin,
A. N. Dyumin, A. V. Morozov, V. A. Smolin, G. V. Tarvid,
and B. B. Tokarev . . . . . . . . . . . . . . . . . . . . . . . . . .
729
268
Using a Linear Polarimeter for Investigating the y Radiation of an
(n, n'-Y) Reaction - L. I. Govor, A. M. Demidov,
0. K. Zhuravlev, V. A. Kurkin, and Yu. K. Cherepantsev . . . . . . .
732
270
Mathematical Modeling of a Nonequilibrium Flow Consisting of Water,
Steam, and Air - N. I. Kolev . . . . . . . . . . . . . . . . . . . .
734
272
LETTERS TO THE EDITOR
Buildup of Radionuclides in Nickel as the Result of Electron and y
Irradiation - N. L. Emets, V. G. Batii, Yu. V. Vladimirov,
Yu. N. Ranyuk, E. A. Shakun, and V. A. Yamnitskii. . . . . . . . . .
742
278
Calculation of the Absorbed Dose of Electron Bremsstrahlung
- V. I. Isaev and V. P. Kovalev . . . . . . . . . . . . . . . . . . .
745
280
Tritium Balance in the Baltic Sea during the Years 1972-1982
- S. M. Bakulovskii and I. Yu. Katrich . . . . . . . . . . . . . .
747
281
The Russian press date (podpisano k pechati) of this issue was
Publication therefore did not occur prior to this date, but must be assumed
to have taken place reasonably soon thereafter.
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POWER STARTUP OF THE IBR-2 REACTOR AND THE FIRST PHYSICS
INVESTIGATIONS IN ITS BEAMS
V.
D.
Anan'ev, V. A. Arkhipov, A. I. Babaev,
UDC 621.039.514.23
Yu.
N.
V.
Yu.
I.
E.
M.
A.
L.
M.
M.
P.
Bulkin, B. N. Bunin, V. S. Dmitriev,
Dollezhal', L. V. Edunov, A. D. Zhirnov,
Lomidze, V. I. Dushchikov, Yu. I. Mityaev,
Ostanevich, Yu. N. Pepelyshev, V. S. Smirnov,
Frank, N. A. Khryastov, Yu. M. Cherkashov,
Shabalin, and Yu. S. Yazvitskii
The powerful pulsed, periodic-action neutron source - IBR-2 [1] - was constructed in the
Neutron Physics Laboratory (NPL) of the Joint Institute of Nuclear Research (JINR) at Dubna.
The reactor was designed for research in the field of nuclear physics, the physics of con-
densed media, molecular biology, the physics of elementary particles (fundamental properties
of the neutron), and also for solving various applied problems by means of neutrons.
Reactors of the IBR type have been developed in the NPL for a long time. It is well
known that modern scientific research on reactors requires a high neutron-flux density. It
is not by chance, therefore, that from the large number of research reactors a group of so-
called high-flux reactors is distinguished, with a maximum thermal neutron flux of 1015 cm 2?
sec-1 (in the Soviet Union SM-2 and the PIK under construction, in the USA - BHFR, and in
France HFR-ILL). These reactors have a high thermal capacity (50-100 MW), with a maximum ac-
ceptable specific power of the fuel. For many technical and economic reasons, it is difficult
to reckon on a significant increase of the neutron flux of stationary reactors. For a wide
class of research, further advancement is possible by the use of pulsed periodic-action sources,
in conjunction with the time-of-flight method. The first reactor of this type with a low
initial power - the IBR-1 - was constructed'at Dubna by the initiative of D. I. Blokhintsev.
Later, it was redesigned as the IBR-30, which has operated successfully up to the present
time. In its parameters and design, the IBR-2 differs considerably from its forerunner, the
IBR-30.
Experience has shown that on a facility of this type problems can be fruitfully solved
which are considered to be traditional for stationary reactors: for example, neutron diffrac-
tion investigations and investigations using the method of small-angle scattering. All the
more, this is related to the study of elastic and inelastic scattering of slow neutrons and
neutron spectroscopic investigations of nuclei. The use of a pulsed fast reactor in conjunc-
tion with the time-of-flight method considerably extends the range of slow-neutron energies
available for experiments.
The pulsed neutron flux of.a reactor of the IBR type should be compared with the steady
flux in a normal reactor. With their equivalence, the reproducibility of the experimental
equipment, positioned in the beams extracted from the reactor, is found to be approximately
identical. Thus, the IBR-30 with an average power of 20 kW is equivalent in its potentiali-
ties to research reactors of megawatt power. This was taken into account in the IBR-2 pro-
ject. With an average power of several megawatts, the pulsed neutron flux of such a reactor
should attain 1016 cm 2?sec-1; i.e., it significantly exceeds the flux of stationary reactors.
In this case, the low average power, by comparison with the power of high-flux reactors, elim-
inates many technological difficulties, in the first place the rapid burnup of nuclear fuel.
Experience in the use of the IBR has allowed the advantages of pulsed sources to be bet-
ter understood, not only for research in the field of neutron spectroscopy of nuclei, but also
in the field of the physics of condensed media. Hence the origination of a number of designs
for powerful pulsed sources on the basis of an accelerator and which, at the present time,
are being built in many countries.
Translated from Atomnaya Energiya, Vol. 57, No. 4, pp. 227-234, October, 1984. Original
article submitted March 13, 1934.
0038-531X/84/5704-0673$08.50 ? 1985 Plenum Publishing Corporation 673
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ylcvivua puL)ilt_.c1L1u115, tui example,
in [1]. Therefore, we shall recall here onlybriefly -~+ .~.. the main structural solutions. The
+
core of the IBR-2 is charged with plutonium dioxide fuel with a total mass of -90 kg. The
fuel elements are cooled by sodium with an inlet temperature of 300?C. The,. cooling. system
is dual circuit, dual loop, with a sodium flow rate of 100 m3/h. The reactor is surrounded
by water neutron moderators (Fig. 1), which are "scanned" by 14 horizontal channels. Two
moderators - "comb-shaped" - have an extended luminescent surface, the shape of which allows
the thermal neutron leakage flux to be increased by a factor of 2 to 3.
The power pulse is shaped by a reactivity modulator (RM), made in the form of two coax-
ially positioned movable neutron reflectors - the main axial movable reflector (MMR), and the
supplementary movable reflector (SMR) (see Fig. 1). The frequency of rotation of the MMR is
1500 min-1. The pulse frequency is varied discretely by means of the SMR, at rest or rotating
with a low speed [2]. In the latter case, the pulse is developed only at the instant of time
when both reflectors are close. to the core. The most important results of the power startup
of the IBR-2 are given below, and experiments are described which are being conducted in its
beams.
Pulsed Characteristics of the Reactor. In 1982, the IBR-2 was brought on an average
power of 2 MW with a rotation frequency of the MNR of 1500 min-1 and a pulse frequency of 25
Hz, which corresponds to a reactor pulsed power of 270 MW. The basic frequency regime of the
reactor, 5 Hz at a power of 2 MW,was achieved in 1984: The peak reactor power attained 1350
MW. The. values of the principal parameters of the IBR-2, obtained at the present time, are
as follows (the error of the neutron flux estimate amounts to 20%):
Average thermal power . . . . . . . . . . . . 2 MW
Power per pulse . . . . . . . . . . . . . . . 1460 MW
Duration of power pulse . . . . . . . . . . . 215 usec
Background power. . . . . . . . . . . . . . 0.1 MW
Duration of thermal neutron pulse in
plane moderator . . . . . . . . . . . . . 230 usec
Thermal neutron flux density:
average with respect to time at the
surface of the plane moderator . . . ... 5.1012 cm2?sec-'
same, peak value . 4.1015 CM-2-sec-1
at the surface of the comb-shaped
moderator. . . . . . . . . . . . . . . 1.1016 cm 2?sec 1
The power startup of the IBR-2 was conducted with a modified reactivity modulator, which
differed from the RM described in [3], in the construction of the SMR. This was done in order
to shorten the power pulse duration of the reactor 0. As is well known, 0 is determined in
the following way:
E _ ('Giav2)1/3, (1)
where a is the coefficient of the parabola describing the change of reactivity during move-
ment of the MMR close to the position corresponding to the maximum reactivity of the reactor,
T is the average lifetime of the prompt neutrons in the reactor, and v is the velocity of the
MMR relative to the core. During the physics startup, it was ascertained that the value of
a, which was in essence the characteristic. of the MMR, depends markedly on the geometry of the
Replacement of.the original version of the SMR made of beryllium by steel in the form
of a trident (it is shown in the front plane of Fig. 1) allowed a to be increased by a factor
of 3. It follows from Table 1 that, taking account of the reduction of T inconsequence of
the additional screening of the core from the external moderators, this gives a fourfold re-
duction of the ratio T/a., which is equivalent to a reduction of the pulse duration by a fac-
tor of 1.6, i.e., down to 140 psec instead of the former 220 psec. However, this advantage
was lost in view of the change to a reduced frequency of rotation of the MMR from 3000 to
-1500 min-1; at the present time 0 = 215 ? 3 psec. A reduction of 0 can be achieved by the
use of a RM of two lattices, rotating contrary to one another [4]. It has been established
experimentally that this modulator provides a power pulse duration of -130 usec, with a rota-
tion frequency of the rotors of 1500 min-1 [5].
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Fig. 1. Schematic diagram of the IBR-2 re-
actor: 1) axial movable reflector (MMR); 2)
supplementary movable reflector (SMR).
.TABLE 1. Power Pulse Duration for Two RM
Versions in the IBR-2
RM version
a, I ? ' x
e, 11sec
x deg-1
1500
m
7- 3 0
min-1
SMR with beryl-
1,0.)-?0,02
80 ?10
360 *
220?5
lium block
SMR in the form
3,00?0,06
63?4
215?3
140 *
of a steel tri-
dent
*Numerical estimate.
The measured shape of the IBR-2 power pulse is close to Gaussian and for the accepted
RH version is almost independent of the operating frequency regime of the reactor. The ratio
of the pulse amplitude to the power background, i.e., the power released between the main
pulses, is equal to 1.3.104. Figure 2 shows the measured. reactor power distribution during
a single pulse repetition interval in the 5-Hz regime. The four additional pulse satellites
are due to the passage of the MMR by the core at the instant when the SMR is not located in
the immediate vicinity of the reactor.
The thermal neutron pulse is formed as a result of moderation of the fast neutrons in
the water moderator surrounding the core. The thermal neutron pulse duration is estimated
approximately by the formula
At- O2 Ate, (2)
where Ato is the thermal neutron pulse duration, originating from the instantaneous fast neu-
tron burst, i.e., when 0 = 0. The amplitude of the thermal neutron flux 0 can be determined
in terms of the ratio of the flux, averaged over time, to the pulse duration At. The parame-
ters of the IBR-2 as a source of slow neutrons have been given previously. Data about the
thermal neutron flux for the IBR-2 are based on the experimental value of the flux density 0
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100 /5D /,;sec
0 15 50 15 /l, m3/'h
1/, 2
611,;;
Hz
Fig. 2 Fig.. 3 Fig. 4
Fig. 2. Powerdistribution for a single pulse repetition interval in the 5-Hz re-
gime, with an average reactor power of 1 MW.
Fig. 3-. Dependence of the reactivity p on the 'so'dium flowrate G fora different
reactor power W. 0 ) W = 0; :0) W = 100 kW.; +) W = 1 MW.
Fig. 4. Spectra of the amplitude fluctuations of the power pulses S WI transverse
vibrations of the MMR, So, and the SMR, Sd, measured in the 5-Hz regime, at an
average reactor power of 1 MW and with a sodium flowrate of 80 m3/h.
at the surface of the plane. moderator, averaged with respect to time, and which was found to
be a factor of 2 higher than the calculated value and equal to 2.5.1012 CM-2 -sec-" at 1-MW
average power.
Power Fluctuations and Other Reactor Parameters. The sensitivity of the periodic-action
pulsed reactor to external reactivity perturbations is determined not by the fraction of de-
layed neutrons Seff, as in a normal reactor, but by the so-called pulsed fraction of delayed
neutrons S , which once again is a factor of 10 less than Seff [1]. Thus, for IBR-2, S =
1.6.10-` keff in the 5-Hz regime and 2.10-4 k in the 25-Hz regime. Therefore, the ques-
tion concerning the fluctuations of a pulsed reactor requires increased attention. With a
relatively high average reactor power, when stochastic fluctuations can be neglected, the
principal contribution to the random deviations of the pulse amplitude from the average value
is made by the vibrations of the RM and fluctuations of the coolant parameters. Fluctuations
of the parameters of other technological systems are small: their total contribution to the
reactivity does not exceed 2.10 6 keff'
The measured power fluctuations of the IBR-2 are considerably lower than the maximum ac-
ceptable. In all the reactor operating regimes investigated, the relative standard deviation
of energy of the -power pulses was found to be within the limits of 1.5-6%.. The power fluc-
tuations increase with increase of the sodium flowrate and the average reactor power.
The fluctuations of the sodium flowrate do not exceed 0.5% and are concentrated mainly
in the region of lower frequencies (less than 1.6-Hz). Variations of the sodium temperature
-at -the reactor inlet are similar to the variations. of white noise, with a,standard deviation
of 0.1?C fora power of l MW, and lead to reactivity fluctuations of ?2.10-6?keff? Approxi-
mately the same reactivity fluctuations are caused by variations of the sodium flowrate, and
the value of the fluctuations is almost .independent-of the reactor power, with a flow rate
close to nominal, Go = 100 m3./h. In.particular, therefore, the angle of slope of the p(G)
curves for G - Go is almost identical for a different reactor power (Fig. 3).
Fluctuations due to the reactivity modulator of the IBR-2 were studied most thoroughly,
and still continue to be studied during operation of the reactor. Figure 4 shows the power
spectrum of the reactor and the.spectra of the transverse mechanical vibrations of the MMR
and the SMR, measured in 1983 in the 5-Hz regime at a power of 1 MW. All.three spectra have
a clearly defined resonance structure. The resonance peaks shown in the figure are charac-,
terized by a frequency measured in hertz, and are explained in the following way: The reso-
nance of 0.8 Hz is due to vibrations of the SMR with a frequency of -84 Hz; the resonance.of
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insignificant wobbles in the transfer units of the kinematic scheme of the RM, occurring with
a frequency of 16.4 Hz. Under the resonance peak of 1.72 Hz, the frequency of the natural
vibrations of the MMR blades is masked, equal to -51 Hz.
No significant variations of the statistical parameters of the RM rotor vibrations and
fluctuations of the reactor power during the time of power startup were observed, although
the fast neutron fluence at the MMR blades attained 3.6.1020 CM-2 . According to the data of
subsequent measurements, the transverse vibrations of the blades of the movable reflectors
on the average (standard deviations) amount to 0.006 mm for the MMR and 0.04 mm for the SMR.
The corresponding reactivity fluctuations should be equal to 3x10-6 keff and 4.10-6 k eff;
however, the total contribution of the MMR and SMR to the reactivity, according to an estimate
by measurements of the power noise, amount to -2.10-6 keff' This is because the vibrations
of the rotors of the MMR and SMR are correlated, as on meeting the latter are displaced to
different sides (they converge).
In the 5-Hz regime, both movable reflectors are rotating, and the angle '1' between the
and SMR at the instant of their meeting can vary with time and thereby directly affects the
reactivity and the pulse duration 0, as the parameter a depends on the relative disposition
of the reflectors. In operating conditions, the angle 7.
The functions f(k) and y(k) do not coincide with the spectrum of the multiplicity of the
particles emitted because several gamma quanta can be incident on a single detector section
or, conversely, one gamma quantum can be recorded in several detector sections. The greater
the differences between the forms f(k) and y(k), the easier the separation of fission events
from capture events and, hence, the greater the accuracy with which a can be determined. The
precision with.which fission events can be separated from capture events depends in many ways
upon the number of sections, the detector volume, the efficiency of recording y quanta, and
several other parameters of the spectrometer of the multiplicity.
In order to illustrate the possibilities of the spectrometer of the multiplicity, the
time-of-flight spectra for the multiplicities k = 4 and k = 10 are shown in Fig. 2. Excel-
lent separation of capture events from fission events is clearly. visible. For example, the
areas of the resonances at E. = 11.66 eV (a z 8.7) and Eo = 12.39 eV (a z 1.6) are about the
same in the spectrum for k = 4, whereas the area of the resonance with a = 8.7 is about 5
times smaller than in the spectrum with k = 10. Resonances with small a values appear more
clearly in the spectrum with k = 10 than in the spectrum with k = 4. The resonance at Eo =
14.02 eV (a z 0.1) can serve as an example.
We selected for evaluation 15 resonances which were well separated on the energy scale.
In the determination of the absolute a value (which we will denote by ao), the numbers rZ and
FZ of the capture events and fission events recorded, respectively, must be known for the
Z-th resonance; in addition, the recording efficiency of capture events (E )and fission (ef)
must be. known. As indicated above, the measurements were made at four threshold values of the
discrimination with respect to the total energy liberated in the detector. When the threshold
was.increased, the efficiency decreased, and therefore in general
i
al = F11 Ili
0
Fvi F;
where j = 1, 2, 3, 4 denotes the number of the discrimination threshold.
Since y(k) an f(k) overlap, an additonal processing of the spectra is required for the
determination of r. and FL Assume that N.(k) events of neutron interactions with nuclei are
recorded with multiplicity k of the Z-th rasonance at the j-th discrimination threshold. The
number N~(k) can be easily obtained from the experimental spectra by determining the area
under a resonance and subtracting the background. In the general case, both F~(k) fission
events and r~(k) capture events are recorded with multiplicity k.
We use the concept of forms and set
1 (k) = I'il'i (k);
(2)
r, (k) Fif1(k).,
Ni(k)=I'iy1.(k)+F)f1(k).
The problem is therefore reduced to the determination of ri and FZ from an experimental
N(k) value. It is also known that the forms y.(k) and .f.(.k) are the lame for all resonances
(home dependence of the-form of the capture upon the spin3of a level will be considered be-
low).. As will be shown below, at multiplicities'k > 10 capture:-events are not.recorded, i.e.,
y(k) = O:for-all-k > 10. This-means that
kI o Ni (k) = Fi k o fi (k)
N~ (k)
~' f1(k)
k~10
(5)
Declassified and Approved For Release 2013/02/22 : CIA-RDP10-02196R000300050004-3
 Declassified and Approved For Release 2013/02/22 : CIA-RDP10-02196R000300050004-3
E 11(2)
k>m upon the Limits of Summation
r1(
ul NMI U, A (=)
NO) / N(2)
l,>rn Ir?r1(
u
I;>m k'Tn,
1
0,37
H
(i,U8
2
0,37
0
1,07
3
(1,34
10
0,0(i
4
0,29
11
11,111;
5
(1,22
12
11,116
6
11,15
13
0,;11;
7
0,11
11;
11,1(6
The r value can be calculated with Eq. (3) in any given interval between k, and k2:
k, k,
Ni (k) - F J 1 (k) ] .
1, (k) k=:k, k=-k,
When the rZ are calculated, the first multiplicity is conveniently omitted (i.e., k.,= 2 is
assumed) because the main part of the background events and only 3% of the total effect are
concentrated in the first multiplicity. The k, value was assumed equal to 6 because only 8%
of all capture events and the major part of the fission events (>80%) are recorded at k > 6.
Let us show that Eq. (5) holds, i.e., that really only fission events are recorded at
multiplicities k > 10. Let us consider the two resonances Z = 1 and Z = 2. We form the ra-
m
tio N'(k)I N2(k) and analyze how it changes with a variation of the limits of summation
(m = 1, 2, ...). We omit the subscript j and indicate the values obtained for j = 1; the
spectra for all thresholds 6 are treated in the same way. The results are listed in Table 1
for the resonances with Eo(1)= 11.66 eV and Eo(2) = 8.78 eV.
We use Eq. (3) and write
1] N(k) r,r> 71, y (k)-(- F>'> Y, 1 (k)
k~_>m k'm k>m
2 Nc2> (k) r 1] ? (4)+F>'> E 1 (k)
k_>m h,m kin
It follows from Table 1 that the ratio no.longer changes for k > 9. Since the forms
y(k) and f(k) differ and since fission is recorded with greater probability at high multi-
plicities, the behavior of the ratio can be explained only by a lack of fission-event record-
ings at k > 10, i.e., we have y(k) = 0 for k > 10. This had to be shown.
We term the range with k > 10 the range of " pure fission." It is then easy to determine
the ratio of the fission events recorded at the two resonances:
N,'> (k)
F"> k->10
_ " N>21 (k)
k> 10
One-must know y(k) and f(k) for determining F Z and P Z from Eqs. (5) and (6). For deter-
mining these quantities, two resonances with different a values are employed. We write down
Eq. (3) for these resonances:
N,i> (k) = I">>y (k) + P" I (k);
N,2> (k) = F>2'T (k) + Flt>1 (k).
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 Declassified and Approved For Release 2013/02/22 : CIA-RDP10-02196R000300050004-3
By mu F_" SUb ILLG --- vi i. iac ac cgUa~tvua w.i~.ii Lllc /1 - atiu JuuLract-
ing the result from the first equation, we obtain
N11'. (k) - vN`2, (k) _ (F?, _ AT 121) 1 (k)
After summation over all multiplicities and taking into account that 7 / (k) = 1 , we obtain
k=1
F`)_ -,,F 12, - Ei [N