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I

LOS ALAMOS SCIENTIFIC LABORATORY

OF THE UNIVERSITYOF CALIFORNIAo LOSALAMOS NEW MEXICO

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ENERGY AND TIME DEPENDENCE OF

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LEGAL NOTICE

.4

This report was prepared as an account of Government sponsored work. Neither the United States, nor the

Commission, nor any person acting on behalf of the Commission:

A. Makes any warranty or representation, expressed

or implied, with respect to the accuracy, completeness, or

usefulness of the information contained in this report, or

that the use of any information, apparatus, method, or process disclosed in this report may not infringe privately

owned rights; or

B. Assumes any liabilities with respect to the use

of, or for damages resulting from the use of any information, apparatus, method, or process disclosed in this report.

As used in the above, “person acting on behalf of the

Commission” includes any employee or contractor of the

Commission, or employee of such contractor, to the extent

that such employee or contractor of the Commission, or

employee of such contractor prepares, disseminates, or

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Printed in USA Price $ 1.00. Available from the

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U. S. Department of Commerce

Washington 25, D. C.
LAMs-2642

PHYSICS

(TID-4500, 17th Ed.)

LOS ALAMOS SCIENTIFIC LABORATORY

OF THE UNIVERSITYOF CALIFORNIA LOS ALAMOS NEW MEXICO

REPORT WRITTEN. January 1962

REPORT DETRIBUTED: JUIY6, 1962

ENERGY AND TIME DEPENDENCE OF

DELAYED GAMMAS FROM FISSION

Work done by: Report written by

Members of Group N-2 L. B. Engle

P. C. Fisher (now with Lockheed P. C. Fisher

Missiles and Space Division)

L. B. Engle

M. P. Kellogg

_,

~—=, !

====

—~

.~a

z~a : I

;z~ <= Contract W-7405 -ENG. 36 with the U. S. Atomic Energy Commission

:=8 , ,

g-co

;~m===m All I.uIMS reports are informal decuments, usually prepared for a special purpose and primarily prepared for use within the Laboratory rather than for

l=” general distrilxitlon, Thie repert has not heen edited, reviewed, or verified

~CO for accuraoy. AU LAMS reports express the views of the authore ae of the

—’

time they were written and do net necessarily reflect the opinione of the Los

Alaxnos Scientific Laboratory or the final opinion of the authors on the subject. —

1

ABSTRACT

This report contains some results of an experiment

designed to measure the energy and time dependence of the

gammas emitted after effectively instantaneous neutroninduced fission of Th 232

, U233, U235, U238, and PU239.

Seventeen-bin distributions of the absolute number of

photons/fission-sec-Mev and intercomparisons and integrations over energy and time of these distributions are

given. Gammas having energies between 0.12 and 6.5 Mev

were detected during five short time intervals between

0.2 sec and 45 sec after fission occurred.

TABLE OF CONTENTS

Page

ABSTRACT . .

INTRODUCTION

REFERENCES .

1.

2.

3.

40

5.

. . . .

.*.O

. ..*

. . . . . .

. . . . . .

. . . . . .

. . . . .

. ...”.

. . . . .

● 0

. .

. .

Bin Widths and Midpoints in Mev for Photon

Spectra . . . . . . . . . . . . . . . . .

●

✎

✎

✎

Distribution of Photons/Fission-sec-Mev for

the Different Time Intervals Following

Th232 Fission . . . . . . . . . . . . . . .

Distribution of Photons/Fission-sec-Mev for

the Different Time Intervals Following

U233 Fission. . . . . . . . . . . . . . . .

Distribution of Photons/Fission-sec-Mev for

the Different Time Intervals Following

~235 Fission . . . . . . . . . . . . . . .

Distribution of Photons/Fission-sec-Mev for

the Different Time Intervals Following

~238 Fission. . . . . . . . . . . . . . . .

.

.

.

.

.

●

✎

✎

.

.

.

.

.

●

✎

●

. 3

. 9

. 12

. 13

. 15

● 19

. 23

. 27

5
TABLES (Continued)

Page

6. Distribution of Photons/Fission-sec-Mev for

the Different Time Intervals Following

-239 Fission . . . . . . . . . . . . . . . . . .31

7. Results of Delayed Gamma Spectra Integrated

over Energy for Different Time Intervals

after Fission . . . . . . . . . . . . . . . . . .39

8. Results of Delayed Gamma Spectra Integrated

over Energy and Time from 0.20 to 45.0 sec

after Fission . . . . . . . . . . . . . . . . . ● 41

FIGURES

1. Pulse height distribution of gammas for different

time intervals following Th 232 fission . . . . . . 14

2. Photon spectra of gammas for different time

intervals following Th 232 fission . . . . . . . . 16

3. Ratios of Th232 photon spectra at all time

intervals . . . . . . . . . . . . . . . . . . . .17

4. Pulse height distribution of gammas for different

time intervals following U

233 fission . . . . . . 18

5. Photon spectra of gammas for different time

intervals following U

233 fission . . . . . . . . .20

6
6.

7.

8.

9.

10.

11.

12.

13.

14.

15.

16.

FIGURES

Ratios of U233 photon

(Continued)

Page

spectra at all time

intervals . . . . . . . . . . . . . . . . . . . .21

Pulse height distribution of gammas for different

time intervals following U

235 fission . . . . . . 22

Photon spectra of gammas for different time

235 intervals following U fission . . . . . . . . .24

Ratios of U235 photon spectra at all time

intervals . . . . . . . . . . . . . . . . . . . .25

Pulse height distribution of gammas for different

time intervals following

Photon spectra of gammas

238 intervals following U

U238 fission . . . . . . 26

for different time

fission . . . . . . . . .28

Ratios of U

238 photon spectra at all time

intervals . . . . . . . . . . . . . . . . . . . . 29

Pulse height distribution of gammas for different

time intervals following Pu 239 fission . . . . . . 30

Photon spectra of gammas for different time

intervals

Ratios of

intervals

Ratios of

following Pu 239 fission . . . . . . . . 32

PU239 photon spectra at all time

● ..*.. . . . . . . . . . . . . . . 33

photon spectra for all isotopes at

0.2 to 0.5 sec interval . . . . . . . . . . . . . 34

7
FIGURES (Continued)

Page

17. Ratios of photon spectra for all isotopes at

1.0 to 2oOsec interval . . . . . . . . . . . . . 35

18. Ratios of photon spectra for all isotopes at

4.0 to 5.5 sec interval . . . . . . . . . . . . . 36

19. Ratios of photon spectra for all isotopes at

10.0 to 13.0 sec interval . . . . . . . . . . . . 37

20. Ratios of photon spectra for all isotopes at

35.0 to 45.0 sec interval . . . . . . . . . . . . 38

21. Comparison of photon spectra integrated over

energy for the different time intervals

after fission . . . . . . . . . . . . . . . . . . 40

8
INTRODUCTION

The purpose of this report is to make available

information derived from delayed gamma measurements.

Results are presented as the energy dependence of gammas

in several time intervals following the fission of various

isotopes. The comments and explanations pertaining to

experimental procedures and to analysis of data, from

which these results were obtained, will appear later in

several detailed articles. Integrated results will be

extended to about 250 seconds after fission, representing

200 sec of data which do not appear in this report.

In the experiment, a sample of material was placed

near the center of the Godiva II critical assembly.

Following irradiation by a less than 0.05-sec-long burst

of fission spectrum neutrons, the sample was pneumatically

transferred to a counting geometry containing a 4 in. x

4 in. NaI crystal. The pulses from the crystal were

recorded in a 100-channel analyzer for time intervals of

0.2 to 0.5, 1 to 2, 4 to 5.5, 10 to 13, and 35 to 45 sec

after fission. Overlapping sets of pulse-height-analyzer

data were used to suitably cover the large range of

9
counting rates present in a given photon spectrum. In

addition to these energy spectra, the time decay of gammas

above several fixed pulse-height biases was followed from

0.3 sec to 300 sec after fission. However, no time decay

data are given in this report.

Normalization of the 100-channel data was accomplished

by radiochemical determination of the absolute number of

fissions responsible for a measured number of counts in a

given pulse-height interval during a given time interval

after fission. A seventeen-bin NaI crystal response

function was constructed from the results of gamma measurements made from radioactive sources of known strength and

from several (p,q) reactions. Photon spectra were derived

by applying this crystal-response function to the pulseheight data.

The figures and tables grouped together at the end of

this report consist of data related to the various photon

spectra measured. Table 1 lists the parameters for the

seventeen-bin photon intervals. The original pulse height

232 233 235

distributions for the isotopes Th , U , U , U

238

, and

~239

are given in Figures 1, 4, 7, 10, and 13, respectively . Tabular and graphical results for the distribution of

photons/fission-sec-Mev with time are given in Tables 2

through 6 and Figures 2, 5, 8, 11, and 14. The relative

10
hardness of a given isotope’s spectra at different times

is shown in Figures 3, 6, 9, 12, and 150 These ratios were

obtained by dividing the spectrum for a given time interval

by the spectrum for the 0.2 to 0.5 sec interval.

Comparison of the spectra for different isotopes at a

given time interval after fission appear in Figures 16, 17,

18, 19, and 20. The results for spectra integrated over

energy appear in Table 7. Table 8 lists both the total

delayed-gamma energy per fission and the total number of

delayed gammas per fission emitted by the different

isotopes. As mentioned earlier, only photons having

energies greater than 0.12 Mev were measured. Sufficient

time decay data exist to allow calculation of the total

number of photons emitted between 0.2 sec and about 250 sec

after fission. However, the results in Table 8 apply only

to those photons emitted between 0.2 sec and 45 sec after

fission.

Only qualitative estimates for the experimental error

have been computed. These estimates indicate a maximum

standard deviation of *15% for all but the Pu 239 numbers,

to which a value of *25% applies.

A few further details concerning this experiment can

be obtained by consulting the references.

11
REFERENCES

R. B. Leachman, Neutrons and Radiations from Fission,

describing the work of Fisher and Koontz in Proceedings of the Second United Nations International

Conference on the Peaceful Uses of Atomic Energy,

Geneva 1958, P/665, Vol, 15, pp 331, United Nations,

New York (1958).

P. C. Fisher, M. P. Kellogg, P. G. Koontz, L. B. Engle,

Delayed Gammas from Fission of Th232, U235, U238, and

~239

9 Bull. Am. Phys. Sot. Ser. II, ~, 31, 1959.

P. C. Fisher, L. B. Engle, Delayed Gammas from Fission I,

Bull. Am. Phys. Sot. Ser. II, Q, 307, 1961.

L. B. Engle, P. C. Fisher, Delayed Gammas from Fission II,

Bull. Am. Phys. Sot. Ser. II, Q, 308, 1961.

12
Table 1

Bin Widths and Midpoints in Mev for Photon Spectra

Bin

1

2

3

4

5

6

7

,

8

9

10

11

12

13

14

15

16

17

AE (Mev)

0.137 - 0.213

0.213 - 0.309

0.309 - 0.428

0.428 - 0.575

0.575 - 0.749

0.749 - 0.954

0.954 - 1.195

1.195 - 1.478

1.478 - 1.808

1.808 - 2.189

2.189 - 2.620

2.620 - 3.110

3.110 - 3.655

3.655 - 4.257

4.257 - 4.918

4.918 - 5.636

5.636 - 6.419

Midpoint (Mev)

0.175

0.261

0.369

0.502

0.662

0.852

1.075

1.337

1.643

1.998

2.405

2.865

3.383

3.956

4.587

5.277

6.028

13
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Pulse Height -Mev Equivalent

Figure 1. Pulse height distribution of

5

aromas for different

time intervals following Th23 fission

14
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m I 1 1 L .

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I 1

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I

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I_

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I

m *4.0:5.5 sec

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~ 35. O-45,0sec I I I I I I

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Photon Energy - Mev

Figure 2. Photon spectra of gammas for different time

intervals following Th232 fission

16
1.0

.—

.-

LL\

u)

c

2

0

-c

a

0.0,

I

1

L) I 2 3 4:

Photon Energy- Mev

%= 1.0-2,0

I sec

4.0-5.5

sec

110.0-13.0

I

sec

35.0-45.(

sec

6 7

Figure 3. Ratios of Th232 photon spectra at all time

intervals

17
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Pulse Height -Mev Equivalent

Figure 4. Pulse height distribution of gammas for different

time intervals following U233 fission
1+

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1,0-2.0 sec —----

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t35.0-45. Osec

Photon Energy -Mev

Figure 5. Photon spectra of gammas for different time

intervals following U233 fission

20
1.(

0,

z=

I

I

+

I

I

I ,

I

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L --

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3 4

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Photon Energy - Mev

~0.2-0.5sec -

1

*

I

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Figure 6. Ratios of U233 photon spectra at all time

intervals

21
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Figure 7. Pulse height distribution of gammas for different

time intervals following U235 fission

22
u

l-l

I-I SINNNN NINalmm(q Comwww

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Photon Energy - Mev

Figure 8. Photon spectra of gammas for different time

intervals following U235 fission

24
n

I

8

c

o.-

(II

(n

1.0

0.1

l--

!

0

al

(n

I

c

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ln

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n

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4 5 6

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I

4,0-5,5 sec

t

10.0 -13.0 sec

I

I II II II

I I —

I

I

1 35-45 sec -

3 4 5 6 7

Photon Energy- Mev

Figure 9. Ratios of U235 photon spectra at all time

intervals

25
tia)(n

L

o.—0-)

(n

,O-’d

1 I I I 1 , 1 , I I , ,

1

! t I I I I I 1 I I -= 1

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Pulse Height -Mev Equivalent

Figure 10. Pulse height distribution of gammas for different

time intervals following U238 fission

26
o q .

m o

l-l 1+

1% x

In

o ~

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Photon Energy- Mev

Figure 11. Photon spectra of gammas for different time

intervals following U238 fission
-

I.(

o.

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Photon Energy - Mev

12. Ratios of U238 photon

intervals
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Figure 13. Pulse height distribution of

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aromas for different

time intervals following Pu23 fission

30

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Photon Energy-Mev

Figure 14. Photon spectra of gammas for different time

intervals following PU239 fission

32
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Photon Energy - Mev

Figure 15. Ratios of PU239 photon spectra at all time

intervals

33
-

Ic

I .0

238

232

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2

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3 4 5

Photon Energy - Mev

of photon spectra

0.5 sec interval

for all

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isotopes

34
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Photon Energy - Mev

Figure 17. Ratios of photon spectra for all isotopes at

l.O to 2.0 sec interval

35
10

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5 6

Photon Energy - Mev

Figure 18. Ratios of photon spectra for all isotopes at

4.0 to 5.5 sec interval

36
I.0

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Photon Energy - Mev

Figure 19. Ratios of photon spectra for all isotopes at

10.O to 13.0 sec interval

37
[c

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Figure 20. Ratios of photon spectra for all isotopes at

35.0 to 45.0 sec interval
Table 7

Results of Delayed Gamma Spectra Integrated

over Energy for Different Time Intervals

after Fission

Isotope

232

233

235

238

239

Time Interval

0.2-0.5 sec

1.0-2.0 sec

4.0-5.5 sec

10.0-13.0 sec

35.0-45.0 sec

0.2-0.5 sec

1.0-2.0 sec

4.0-5.5 sec

10.0-13.0 sec

35.0-45.0 sec

0.2-0.5 sec

1.0-2.0 sec

4.0-5.5 sec

10.0-13.0 sec

35.0-45.0 sec

0.2-0.5 sec

1.0-2.0 sec

4.0-5.5 sec

10.0-13.0 sec

35.0-45.0 sec

0.2-0.5 sec

1.0-2.0 sec

4.0-5.5 sec

10.0-13.0 sec

35.0-45.0 sec

Photons/

Fission-See

0.966

0.487

0.267

0.118

0.0343

0.312

0.189

0.0958

0.0490

0.0161

0,613

0.324

0.169

0.0775

0.0225

1.42

0.636

0.289

0.110

0.0303

0.608

0.344

0.166

0.0746

0.0209

Mev/

Fission-See

0.916

0.501

0.246

0.112

0.0343

0.303

0.177

0.0885

0.0465

0.0161

0.564

0.311

0.153

0.0706

0.0221

1.32

0.618

0.255

0.0988

0.0281

0.529

0.296

0.138

0.0624

0.0197

39

Mev/

Photon

0.948

1.029

0.921

0.949

1.000

0.971

0.937

0.924

0.949

1.000

0.920

0.960

0.905

0.911

0.982

0.930

0.972

0.882

0.898

0.927

0.870

0.860

0.831

0.836

0.943
1“I

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...

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II 1:

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-b

$4

vi
I Table 8

Results of Delayed Gamma Spectra Integrated over

Energy and Time from 0.20 to 45.0 sec after Fission

Isotope Photons/Fission Mev/Fission Mev/Photon

232 5.07 5.04 0.994

233 2.02 1.97 0.975

235 3.31 3.18 0.961

238 5.50 5.08 0.924

239 3.26 2.86 0.877

41