AE-19

Sources of gamma radiation

in a reactor core

Matts Roas

AKTIEBOLAGET ATOMENERGI

STOCKHOLM • S\\ HDJtN • 1959

AE-19

ERRATUM

The spectrum in Fig. 3 has erroneously been normalized

to 7. 4 MeV/capture. The correct spectrum can be found by mul-

tiplying the ordinate by 0. 64.

AE-19

Sources of gamma radiation in a reactor core

Matts Roos

Summary: -

In a thermal reactor the gamma ray sources of importance for

shielding calculations and related aspects are 1) fission, 2) decay of

fission products, 3) capture processes in fuel, poison and other

materials, 4) inelastic scattering in the fuel and 5) decay of capture

products. The energy release and the gamma ray spectra of these

sources have been compiled or estimated from the latest information

available, and the results are presented in a general way to permit235

application to any thermal reactor, fueled with a mixture of U and238U • As an example the total spectrum and the spectrum of radiation

escaping from a fuel rod in the Swedish R3-reactor are presented.

Completion of manuscript April 1959Printed Maj 1959

LIST OF CONTENTS

Page

Introduction . . . . . . . . . . . 1

1. Prompt fis sion gamma rays i

2. Fission product gamma rays 2

3. Uranium capture gamma rays 4O -2 Q

4. U inelastic scattering gamma rays 5

5. Gamma rays from capture in poison, construction

materials and moderator . . . . . * • » . . • . . . . . . . . 8

6. Gamma rays from disintegration of capture products. . 8

7. Total gamma spectra. Application to the SwedishR3 -reactor 9

SOURCES OF GAMMA RADIATION IN A REACTOR CORE.

INTRODUCTION

In reactor shielding studies and related aspects it is of

importance to know the energy released as gamma radiation and

its spectral distribution. So far detailed calculations of the total

spectrum of gamma radiation from a reactor core have been

hampered by a very limited knowledge of the sources. However,

the large volume of relevant information published during 1958,

especially concerning the main sources, now facilitates an esti-

mate based on fewer guesses than before.

The gamma ray spectra of different sources can most con-

veniently be compared when expressed in units of energy release

per fission per energy interval^ or MeV/f. MeV, and the integrated

spectra thus in MeV/f. However, only the spectra of prompt fission

and fission product radiations can without loss of generality be ex-

pressed in these units, whereas in capture processes, for instance,

the number of captures cannot be related to the number of fissions

without reference to a specific reactor. In order to show the rela-

tive importance of the different sources, we therefore in the last

section apply the general results to a particular reactor, the

Swedish R3 (MARGEN & al. 1958), for which we give the total

spectrum and the spectrum of radiation escaping from a fuel rod.

1. PROMPT FISSION GAMMA RAYS

The spectrum of y-rays emitted within 5» 10 s of fission

has been measured in the energy ranges from 0.3 MeV to about

7.3 MeV by MAIENSCHEIN & aL(i958), from 0.015 MeV to

0.800 MeV by VOITOVETSKII & aL(l957) and from about 0.020

MeV to about 0.260 MeV by SKLIAREVSKII & aL (1957). It seems

possible to join the spectra of MAIENSCHEIN and SKLIAREVSKII

in the region between 0.26 MeV and 0.30 MeV, whereas the

spectrum of VOITOVETSKII matches the spectrum of SKLIAREVSKII

only at the softest gamma line (0. 03 MeV)s falling a factor 5 below

at 0.20 MeV and a factor 10 lower than MAIENSCHEIN ' s spectrum

in the region from 0. 30 MeV to 0. 60 MeV._ Q

The energy re leased within 5*10 s of fission and within the

energy range 0.3 - 10 MeV (extrapolated from 7,3 MeV to 10 MeV)

is repor ted by MAIENSCHEIN to be 7.2 ± 0. 8 MeV/f, and within the

range 0. 015 - 0.260 MeV by SKLIAREVSKII to be about 0.24 ± 0. 05

MeV/f. In addition MAIENSCHEIN has found delayed gamma rays inQ L

the region between 5*10 s and 10 s after fission8 and in the energy

range 0 . 1 - 2 MeV. The intensity is reported to be (5. 7 ± 0. 3) % of

the prompt radiation, or about 0, 4 MeV/f. Thus the total energy

released within 10 s is about7.9 MeV/f (1.1)

The spectrum shown in Fig.l is obtained by joining the spectra

of MAIENSCHEIN and SKLIAREVSKII, and is, to account for the

unknown spectrum of delayed gamma raysj normalized to 7.9 MeV/f.

2. FISSION PRODUCT GAMMA RAYS

Several reports ( BLOMEKE and TODD 1957, KNABE and

PUTNAM 1958, MAIENSCHEIN & al. 1958, MILLER 1957, PERKINS

and KING 1958, PRAWITZ & al. 1958, SCOLES 1958 a,b, STEHN and

CLANCY 195 8 ) have recently been published on the gamma-radiation

of products of thermal fission of U at various cooling times after

irradiation times of various durations. The reports of BLOMEKE

and TODD, MILLER, SCOLES, PRAWITZ & al. , and PERKINS

and KING are based on available chemical data and thus do not ex-

tend to very short cooling times. As the most short-lived isotopes

emit comparatively hard v-radiationj it is recognized that the extra-

polation of decay curves down to zero cooling time might give results

which are too small by a factor of 4. It could be possible, however,

to obtain better agreement by taking into account new nuclear data

on very short-lived isotopes^ as reported for instance by O'KELLEY

& al. (1958).

MAIENSCHEIN 8t al. have measured the Y~ray spectra at

various cooling times down to about 1 second after irradiation for

time intervals sufficiently short to be considered instantaneous.

These values appear to give the best starting point at present in

an effort to evaluate the spectrum at zero cooling time and infinite

irradiation time. (There is essentially no change in the spectrum

between an irradiation time of a few hundred days and infinity,

for most reactors.) The total energy above 0.3 MeV emitted be-Q

tween 1 s and 10 s after fission is reported to be 5.9 i 0.7 MeV/f

(MAIENSCHEIN has used the chemical data of PERKINS and KING3 8

for extrapolation from 1.8» 10 s to 1 0 s). Extrapolating in

MAIENSCHEIN ' s curve from 1 s down to zero, one obtains an

increment of about 0.3 MeV/f. An estimate of the contribution from

energies < 0. 3 MeV can be based on the lowest energy group of

PERKINS and KING which extends down to 0.1 MeV. This gives

an additional increment of about 0. 3 MeV/fa bringing the total

energy release up to 6. 5 +. 0.7 MeV/f.

STEHN and CLANCY have made an extensive survey over

several measurements on (3- and v-activities at very short cooling

times (this survey includes some of the results reported by

MAIENSCHEIN)8 and they conclude that a reasonable value for the

total v -energy released would be about 7.0 MeV/f.

From the standpoint of shielding this value is slightly more

conservative than the value of MAIENSCHEIN. It thus seems reason-

able to adopt it at present.

The fission product v-ray spectrum at zero cooling time and

infinite irradiation timej Fig. 2, has been constructed in the follow-

ing way:

The energy release in each of the 6 energy groups is obtained

by extrapolating the photon-intensity time distributions of MAIEN-

SCHEIN from 1 s to zero, integrating from zero to 1800 s, adding

a contribution for the time between 1800 s and 5* 10 s (it was

necessary to calculate this separately from the data of BLOMEKE

and TODD, for each isotope present and each gamma line, because

the similar calculations published by PERKINS and KING have an

energy grouping different from MAIENSCHEIN and are thus difficult

1) KNABE and PUTNAM give 6. 6 MeV/f for photons of energy > 0. 1MeV released between Is and 10^ s.

to compare), multiplying by the group width and by the average

energy of the group. The average energy was estimated from the

continuous belt measurements of MAIENSCHEIN. The sum of the

6 groups, covering the energy range 0.3 - 5.0 MeV is found to be

6.5 MeV/f. This figure can be compared with the figure 5.9 i 0.7

MeV/f of MAIENSCHEIN plus the estimated contribution of energy

released within i s of fission, 0.3 MeV/f. The difference 6 . 5 - 5 . 9

0.3 = 0.3 MeV/f is probably attributable to the fact that the photon

intensity time-distributions are uncorrected for the spectrometer

response function, whereas the total energy release curve has an

approximate correction.

To the histogram of the 6 energy groups we finally add the

estimated 0.3 MeV/f in the region < 0.3 MeV. The spectrum is

obtained by fitting the histogram with a continuous curve in such

a way, that within each group the shape of the spectrum resembles

that of the corresponding part of the spectrum from the continuous

belt measurements, and the curve is normalized to 7.0 MeV/f.

3. URANIUM CAPTURE GAMMA RAYS

238The (n, Y)~sPectrum of U has been investigated by

BARTHOLOMEW and HIGGS (1958). In the low energy region

SCHULTZ & al. (1957) have presented measurements on natural

uranium9 but their paper gives the intensity only on a relativeZ38

scale, and is therefore difficult to relate to the U spectrum of

BARTHOLOMEW and HIGGS. In Fig. 3 we have reproduced the

spectrum of BARTHOLOMEW and HIGGS, after normalizing it239

to the last-neutron binding energy of U f

4.70 MeV/capture . (3.1)

235The gamma ray spectrum from capture in U has nots to

our knowledge, been measured. It has been conjectured by

BERTINI & al. (195 6) to use the same spectral distribution as for

prompt fission gamma rays. On the other hand GROSHEV & al.

(1958) have investigated the general shape of the unresolved part

of (n, v)-spectra for different compound nuclei of the same proton-

neutron parity. For even-even nuclei like U , they show that

the continuous spectra start roughly at 1,5 MeV below the binding

energys increase to a maximum at about 2 or 3 MeV and then

decrease to zero. On this very approximate basisone can constructO O c O O £

a spectrum for U ( 1*'Y) U and normalize it to the bindning

energy

6.42 MeV/capture. (3.2)

7 ~\R4. U INELASTIC SCATTERING GAMMA RAYS

The differential inelastic scattering cross-sectionsO T Q

cr(E t E , 9) of the energy levels E g. 1.75 MeV of U haveo

been measured at 9 =90 for neutrons of energies E <. 2 MeV

by CRANBERG and LEVIN (1958). The integral inelastic scattering

cross-sections cr(E , E ) of the energy levels E s which for most

energies E are equal to 4 7T<r(E , E , TT/2), have been calculated

by MANDEVILLE and KAVANAGH (1958), who have completed the

cross-section table of CRANBERG and LEVIN by some theoretically

deduced values.

Although the values of cr(E , E ) are given only for a few

neutron energies E , <r(E , E ) can be plotted for each E as a

function of E »if the total inelastic scattering cross-section

<r (E ) = / <r (E , E )v n' l_j v y* n'

is known. Compilations of data on<r(E ) (CRANBERG and LEVIN,

HUGHES and SCHWARTZ 1958) cover the energy range E ^ 2 , 5

MeVj at 3.5 MeV it is possible to obtain a point at 3. 1 barns from

a comparison of the integrals of the spectra of inelastically

scattered 2.5 MeV and 3.5 MeV neutrons» as reported by FETISOV

(1957). It thus seems that the total cross-section <r(E ) levels off

to about 3 barns at energies E > 2 MeV. The plots of <r(E , E )

and 2(E ) are shown in Fig. 4.

For E < 2 MeV the intensity of each gamma line (of energy

E ) is represented by the integral

1) In his recent compilation HOWERTON (1958) suggests about2.5 barns. When this value is inserted in (4. 8), the figure0. 8 MeV/f in table 2 changes to 0. 7 MeV/f.

MeV

O

a jyiev

E \ N(E )P [rS(E , E )] dE , (4.1)V j n ' c L V Y n n

where

v • N(E ) = uncollided fission neutron spectrum»)

P [ r S ( E ) E )] = probability that a neutron of energy E

23 8collides with a U -atom and excites the E - level , and

r = radius of the fuel e lement .

The intensity is obtained in MeV/f j however, both S(E , E )

and r a r e dependent on the choice of reac tor and fuel e lements , and

the integration will therefore be left to the las t sect ion.

The hardes t gamma line of CRANBERG and LEVIN is actually

not one line but a number of lines ar i s ing from severa l energy levels

between 1.4 and 1.75 MeV. At sti l l higher energies the level density

i n c r e a s e s and the s ta t is t ica l theory should become applicable. F r o m

the review ar t ic le of KINSEY (1957), assuming a constant c r o s s -

section cr(E ) = a" in the s ta t i s t ica l region^ the spect rum of inelast ical

ly sca t te red neutrons can be expressed as

w(En) , Q

F ( e , E n ) d e = const. ^ E n

+<^ < e e ~ e / de , (4.2)

where

Q = bindning energy of a neutron in the compound nucleus^

co(E ) = const. E ~ ' e n9 the level density at the bombard-

ing energy E ,n E

d n

G =-T=p—In w(E ) = s the nuclear t empera tu ren aVE + 5 / 4 introduced by Weisskopf

and238 — 1 /2

a is a constant^ which for U has the value 5.25 MeV ' <

If we normal ize the spect rum (4. 2) by the requi rement

ErF(e,Ej de = E , (4.3)

n'

we obtain the fraction F(eaE )dedE of all bombarding neutrons

of energy between E and E + dE which are scattered into the6 7 n n nenergy in terva l between e and e + de ,

FfcjEjdedE^ = - n-_— . (4.4).2

)de dEn n

E -E /en \ n'

j _ n \ _ n'9

The total energy released as gamma radiation is then given by an

integral like (4. 1), where E - e is substituted for E , and where

P (r2) now is a constant, since ar was assumed constant in theC

region of interest (E > 2 MeV):

E

f d E n C"

2 MeV n 0

Substitution of (4.4) in (4.5), and integration over the integral in

e gives

-E /9(2+En/9)-(2+3En/9)e n

cv—/ j -v~ n # -p E \ - E / ev - P (rS) \ N(E )• 9 . = 2 ^ _ dE . (4. 6);v ' 1 x n' / E \ -E TB n x '2 MeV 1- ( 1 - - ^ - J e n

In our case E / 9 >5>i (with a minimum value = 8. 67 at 2 MeV) son

that (4. 6) can be simplified to

oo

v P (rS) \ N(E ) (29 + E )dE . (4.7)cx ' J v n' x n' n

2 MeV

The integral has the value 1.61 MeV per inelastically scattered

neutron. When v =2.47 neutrons/f, the expression (4.7) takes me

value

4.0 P (rS) MeV/f- (4.8)

The spectral distribution of this radiation is unknown. If all the

excitation energy were radiated as ground-state transitions

the spectrum would be given by the integrand in (4.7). Since this

is not the case, the spectrum is considerably softer, with a peak

somewhere between 1 and 2 MeV. As a rough estimate we assume

that 3 Pc(r£) MeV/f has the distribution of the integrand in (4.7),

and the remaining quarter is distributed in the region < 2 MeV in

such a way that the spectrum becomes zero at zero energy and is

continuous at 2 MeV.

5. GAMMA RAYS FROM CAPTURE IN POISON» CONSTRUCTION

MATERIALS AND MODERATOR

After short irradiation times almost all the poison in the reactor135

fuel is Xe 3 for which both the capture gamma spectrum and the

total energy release per capture (the binding energy of Xe ) are12 14

unknown. After a year ' s irradiation time in a flux of 1 0 - 1 0

n/cm s the Xe -fraction in the posion is still over 50 %, so that

it is not worthwhile to investigate the spectra of the other poison

components in any detail (BLOMEKE and TODD, 1957).J o /

The binding energy of the two last neutrons in Xe is 14. 5

MeV» which suggests that we adopt the figure8 MeV/capture (5.1)

as the approximate total energy release.

The capture gamma spectra of other absorbers present in the

construction materials, the coolant or the moderator can be found

in the recent compilations of GROSHEV & al. (1959)* BARTHOLOMEW

and HIGGS (1958) or DELOUME (1958).

6. GAMMA RAYS FROM DISINTEGRATION OF CAPTURE

PRODUCTS

_ . t , , TT239 TT236 . __ 136 ,The main capture products are U * U and Xe t of

239which only U is radioactive. In addition there might be radio-

active capture products in the construction materials, the coolant239 239

and the moderator. U disintegrates to Np by emission of one239 239

photon of 0. 074 MeV. Np disintegrates in turn to Pu in acomplicated way, by emission of soft (< 0.35 MeV) gamma rays.

From the decay schemes suggested by STROMINGER & al. (195 8 a, b)

and by DZEPELOV and PEKER (1957) one obtains a total energy

release of approximately 0.4 MeV per disintegration, including239

the single line of U .

At saturation (times large compared with the half-lives239 239

of U t 23.5 m and Np , 2.33 d) every neutron capture in238 2 39

U is followed by one disintegration of a U nucleus and onedisintegration of a Np239

i s

nucleus, so that the net energy release

2380.4 MeV/capture in U

The approximate spectrum is given in table 1 below.

Table 1.

(6.1)

Gamma energy release from disintegration of U239

Energy rangeMeV

0.05 - 0,100.10 - 0.150.15 - 0.200.20 - 0.250.25 - 0.300.30 - 0.35

Energy releaseMeV/capture

0.1090.04600.0910.1250.027

7. TOTAL GAMMA SPECTRA. APPLICATION TO THE

SWEDISH R3-REACTOR

The R3-reactor is a UO9 -fueled, D-, O-mode rated and D,O-Lt Li Lt

cooled reactor to be operated at 125 MW. The fuel elements contain

43. 5 % UO2 by volume, 46.4 % D£O at about 220° C and 10. 1 % Zr,

and they are arranged in the moderator on a square lattice with a

lattice pitch of 27 cm (MARGEN & al. 1958).

In natural uranium, there are238

0.66 thermal captures in U per fission» and

a=0.i9 " " " U " "T i n

The number of neutrons captured in U -resonances per

fission is given (see for instance WEINBERG and WIGNER, 1958,

p. 179) by

10

ve P fP r(i-p) , (7.1)

where

v = Z.47 fission neutrons produced per fission

8 = 1 . 03, the fast fission factor

p = 0.89» the resonance escape probability

P f = the fast non-leakage probability

P = the resonance non-leakage probability

2 -4 -2B a 2.4 • 10 cm 3 the buckling of the reactor core* andT = 160 cm , the Fermi age.

With these values, the expression (7.1) becomes 0.27 captures/f.238 239

The total number of capture reactions U (n, v) U per

fission is thus 0.66 + 0.27 = 0.93 captures/f. This factor and the

figures in (3.1) and (6.1) give238

4. 37 MeV/f released as U capture gamma radiation, and0.37 MeV/f " " U239 decay " "

a times the figure in (3.2) gives-p o r

1.22 MeV/f released as U capture gamma radiation.

The number of neutrons absorbed in poison* construction

materials and moderator per fission is given by

v 1 - fn f - <7'2>

where

— =s 1.85 neutrons absorbed in U per fission, and

f = 0.94, the thermal utilization factor.

With these values, the expression (7.2) becomes 0.12 captures/f.

In order to find the proportions of neutrons absorbed in Xe, Zr and

D?O respectively, we weight the components with the product of

neutron flux and macroscopic cross-section in the homogenized

lattice cells. The cross-section of Xe is given in terms of barns per

original

We find

2 o coriginal number of U atoms, by BLOMEKE and TODD (1957).

0.079 captures in Xe per fission

0.029 " " Zr " "

0.012 " " D " "

I i

Using the binding energies 8 MeV for Xe, 6.97 MeV for Zr and

6.24 MeV for D, the energy release becomes

Xe: 0. 63 MeV/f

Zr: 0.20 "

D,O: 0.07 it

238The contribution from inelastic scattering in U is found

by calculating the collision probability P (r2), which was introducedC

in (4.1). P (r2) has been computed for uniform source strength

distributions and different source geometries by PLACZEK & al.

(1953). For a homogenized fuel element of radius 5. 62 cm the

total energy released in inelastic scattering is found to be 0.8

MeV/f.

In table 2 we collect all gamma sources together and compare

them with a previous calculation by BRAUN (1957) on a similarJ238

reactor. The largest difference is found to arise from the u

capture, where BRAUN has used a binding energy of 7.5 MeV

instead of 4.7 MeVj influenced by the value of the average binding

energy per nucleon (which is approximately 7.5 MeV for U )

and by a gamma line at 7.5 MeV reported by KENNEY and

MATTINGLY (1956), but not found later (BARTHOLOMEW and

HIGGS, 1958).

Table 2.

Total gamma energy release.

Source

Prompt fission

Fission productsTT238U captureTT 2 35U capture

Inelasticscattering

v 1 3 5

Xe capture

Other capture

U decay

Other decay

Total

Energy release (MeV/f)

Present

7.9

7.0

4.37

1.22

0.83>

0.63

0.271)

0.37

22.6

BRAUN

7.8

7.2

j 8.2

0.9

i.o2)

Ö.42)25.5

1) Zr and D2O 2) Al 3) Cf footnote on p. 5.

12

The resulting total spectrum is shown in Fig. 5. The spectrum of

radiation escaping from a fuel rod can be found by multiplying the

total spectrum by the energy-dependent escape probability P (E)

for photons of energy E. P (E) has been investigated by STORY6SC

(1957) for a uniform source strength distribution and for a step-

function approximation to the real source strength distribution in

cylindrical fuel rods.

However, it can be shown in the energy range covered by

STORY» that a simplified calculation taking into account only the

first absorbing collision and assuming a uniform source strength

distribution gives a result which lays well between the maximum

and minimum curves of STORY. The escape probability would thus

be given by

where

P is the collision probability of PLACZEK, and \i (E) is

the energy absorption coefficient for photons of energy E in the

homogenized rod of radius r.

The integral of the spectrum of escaping radiation, shown

in Fig. 5, is found to be 7. 6 MeV/f, which can be compared with

the figure 8. 6 MeV/f of BRAUN. The fraction of gamma energy

escaping from the fuel rod is thus approximately i / 3 .

In table 3 we give the integrals over 8 energy groups of the

spectrum of escaping radiation, S(E)» and the average energies

of these groups, defined as

E. E.

E. = \ S(E) E d E / \ S(E) d E.

i l i

13

Table 3.

Energy groups of the spectrum of escaping radiation.

i

1

2

3

4

5

6

7

8

Total

Energy intervalMeV

0 - 1

1 - 2

2 - 3

3 - 4

4 - 5

5 - 6

6 - 7

7 - 8

0 - 8

E iMeV

0 . 7

1.5

2 . 4

3 . 4

4 . 3

5 . 4

6.2

7 . 4

2 . 1

Released energyMeV/f

1.302.92

1.910.88

0.36

0.88

0.12

0.02

7.59

ACKNOWLEDGEMENTS

For valuable discussions and helpful suggestions the author

is indebted to Messrs. J.S. Story* Harwell, J. Braun and

N. G. Sjöstrand, AB Atomenergi.

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SKLIAREVSKII V.V., FOMENKOD.E. and STEPANOV E. P. (1957)Investigation of 11 35 fission y rays in the energy region up to 250keV. Soviet Physics 5, 2, 220-225. (Russian reference: JETP,

~ 32, 256-262).

STEHNJ.R. and CLANCY E.F. (1958) Fission-product radio-activity and heat generation. Presented at Geneva as P/1071, 1958.

STORM E. , GILBERT E. and ISRAEL H. (1958) Gamma rayabsorption coefficients for elements 1 through 100 derived fromthe theoretical values of the NBS. LA-2237.

STORY J.S. (1957) Escape of gamma radiation from uraniumrods in a pile heat evolved in the moderator. AERE T/R 2218.

STROMINGER D. andHOLLANDER J.M. (1958) Decay schemes.UCRL-8289.

STROMINGER D., HOLLANDER J.M. and SEABORG G. T. (1958)Table of isotopes. Rev. Mod. Phys. 30, 2, II.

SULLIVAN W.H. (1957) Trilinear chart of nuclides. Oak Ridge.

16

WEINBERG A.M. and WIGNER E.P . (1958) The physical theory ofneutron chain reactors. Univ. of Chicago Press.

VOITOVETSKII V.K. , LEVIN B.A. and MARCHENKO E.V. (1957)Soft 15-800 keV radiation accompanying the thermal neutron fissionof uranium. Soviet Physics 5, 2, 184-188 (Russian reference:JETP, 32, 263-268. ~"

MeVf.MtV

J._

4..

3..

2 .

1 .

i

\\V

\

\X

0 f 3 4 S 6 7 6 MeV

Fig. 1. Spectrum of gamma rays emitted promptly (within i O s)

after fission. Normalized to 7.9 MeV/fission.

3

9

1

0

'eV

/

/

//

/

r\\

\\\

-HeV

Fig. 2. Spectrum of gamma rays emitted by U thermal fission

products, after 5»iO s irradiation time and zero cooling time.

Normalized to 7.0 MeV/fission.

3 AfeV

Z38 Z39Fig. 3 U (n»v) U gamma ray spectrurtij normalized to

4.70 MeV/capture.

2p MeV

Fig. 4. Total inelastic scattering cross-sections cr and inelastic

scattering cross-sections <r (E * E ) of gamma energy levels

MeVf.MeV

MeV

11

10

9

8

7

f,

s

4-

J

?

1

0

I

//j

/jj

å

A

\\\ \\ \

v\

•

3

Z

t

0MeV

Fig. 5. A. Spectrum of total gamma energy released in the R3 core

(scale on left).

B. Spectrum of gamma radiation escaped from the R3 fuel

elements (scale on right). The peaks at 4 MeV and 6.25 MeV

Z38are due to capture in U and Ds respectively.

Price Sw. cr. 4: —

Additional copies available at the library ofAB ATOMENERGIStockholm - Sweden

Affärstryck Offset 1959