LA-5662-MSCIC-14 REPORT COLLECTION

REW+G2%JGTIONUC-34C

-ci3 COPYReporting Date: June 1974

. Issued: August 1974

I

Fourteen-MeV, Neutron-Induced Gamma-RayProduction Cross Sections

. ,,.

by

Darrell M. DrakeEdward D. ArthurMyron G. Silbert

)alamosscientific laboratory

of the University of CaliforniaLOS ALAMOS, NEW MEXICO 87544

UNITED STATES

ATOMIC ENERGY COMMISSION

CONTRACT W-740 S-ENG. S6

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FOURTEEN-MEW, NEUTRON-INDUCED GAMMA-RAY

PRODUCTION CROSS SECTIONS

by

Darrell M. Drake, Edward D. Arthur, and Myron G. Silbert—..

,g%; ABSTRACT“!B&l.-l3==—E’ A pulsed 14.2-MeV neutron source and NaI(Tl ) gamma-rayt~:-8

spectrometer were used to measure gamma-ray production cross

E!E;’

sections for carbon, magnesium, aluminum, chromium, iron,nickel, copper, molybdenum, niobium, tantalum, platinum,

~= 235U, and 23%.-l—~mcm:—

.—— ——— ——— ——— ——— ————————

1. INTRODUCTION

Gamma-ray production cross sections weremeasured for samples of carbon, magnesium,aluminum, chromium, iron, nickel, copper,molybdenum, niobium, tantalum , platinum, ‘5U,and 23%% that were bombarded with a pulsed 14.2-MeV neutron beam obtained from the %I(t,n)4Hereaction. These cross sections are of interest forapplications to the controlled thermonuclear reaction(c’I’R) program and to various other Laboratoryprograms.

II. EXPERIMENTAL ARRANGEMENT

Figure 1 shows the experimental arrangement. Achopped beam of tritom (10-ns time width at 2-mHzrepetition rate) was accelerated to 2.3 MeV by theLos Alamos Scientific Laboratory (LASL) VerticalVan de Graaff. The triton beam pulses were con-densed to a time width of 1 IIS and directed into adeuterium gas target. Neutrons, emitted at 90° to thetriton beam with a mean energy of 14.2 MeV, in-teracted with one of the samples placed about 100mm from the neutron source. The energy spread ofthe neutrons intercepted by the samples was about+0.5 MeV. Gamma rays produced from the bom-barded samples were collimated and pulse-heightanalyzed by a heavily shielded NaI(Tl ) crystal andphotomuhiplier system. An anti-Compton NaI(Tl )scintillator surrounding the center crystal was used tosuppress further the background events and to im-prove the response functions. The pulsed neutronbeam allowed time-of-flight (TOF) dkrimination by

sorting out the desired gamma rays from neutron-related and other background events in the crystal.

III. DATA REDUCTION

A. Background Subtraction

Figure 2 shows a relative time spectrum of NaI(Tl)pulses. Time gates were set as indicated to recordpulses with differing time relationships relative to afiducial time signal from a beam pickoff loop. Gate 1covered the time region containing prompt gammarays directly from the sample. Gate 2 was set to covera time region before the neutrons from a pulse hadarrived at the sample and therefore was a measure of

+ IOns

-Te=~=-F=--.-Oeflectorplotes

Buncher

il,-lun’aston shadow bar ,,

1..

Gamma-ray lns~i~ IjmmOuroyfor

sample

\

Time pick off ,~!!

?

rll!lgj

‘“”’”7 i @

/

Neutron sarce (Front view

/

ToP ViSW

Nautron source Tungsten shodow bar

Fig. 1.Experimental arrangement for the measurementsof gamma-ray spectra. i%e detector and sampleare about 100 mm above the plane defined by thebeam path.

1

01 I I I I I I I I I420 5CXY 580 660 740

Fig. 2.Time spectrum of pulses in the gamma-ray detec-tor relative to the beam burst pickoff time. Gate 1corresponds to gamma rays made in the sample dueto the burst of neutrons. Gate 2 corresponds to atime-independent background. Gate 3 correspondsto fast neutron interactions in the NaI crystal.

time-independent background. Gate 3 covered timesafter the direct gamma rays had arrived at the scin-til.later and therefore was assumed to correspond toneutron-related events in the crystal that weredelayed by the neutron TOF.

The first step in data reduction was to subtract thebackground pulse-height spectrum of Gate 2,properly normalized, from the pulse-height spectrumdefined by Gate 1. Next, a separate spectrum,measured with no sample in position and the sametime gates, was subtracted to obtain a net pulse-height spectrum.

The net spectra for the samples used in this experi-ment (except for iron) are shown in Figs. 3 through14. Figure 15 shows the pulse-height spectrum foriron before subtracting the no-sample spectrum. Thisfigure also shows the corresponding no-sample spec-trum. The computer program NIBL converted the netpulse-height spectra to gamma-ray spectra, usingknowledge of the NaI(Tl) spectrometer’s response tomonoenergetic gamma rays.

B. Response Functions

The response functions and efficiencies used inanalyzing the experimental data were obtained bymeasuring the gamma-ray line shapes of calibrated

Gamma-Ra~ Eneray ( MeV)30 I 2 “3-- 4 5

10 I I 1

Corbon‘fl’i

Fig. 3.Net gamma-ray pulse-height spectrum for carbon.

sources over the 0.28- to 4.4-MeV energy range. Theresponse functions are shown in Fig. 16 for 4.4-, 2.75-,1.37-, and 0.66-MeV lines originating from neutron-bombarded carbon, fz4Na, and 13 Cs radioactive

sources. The unfolded spectra (not corrected for ef-ficiency) strongly resemble the net pulse-heightspectra because the response functions have such afavorable peak-to-tail ratio.

The samples used in the collection of experimentaldata influence the shape of the gamma-ray responsefunction; therefore, the response measurements weremade so as to account for these sample-dependenteffects. For example, Fig. 17 shows the gamma-ray

,.40 I 2GmTInp-R.~ Energy (Me{) 7 ,

I I # o [ 1 I r<

Magnesium

110’I , t I

o 40 80 120 160 2(XI 240 280Channel

*

.

Fig. 4.Net gamma-ray pulse-height spectrum formagnesium.

2

f

-J

Gamma Ray Energy (MeV)

103;I 2 3 4 5 6 7

.

; ‘ ‘?’ ‘“/

Aluminum

●

.

$,.2. . “.J-+QI_ ,

zo “ +--

k“

I.

--i10’

111 1 1 1 I t 1 1 ! 1 I0 40 80 120 160 200 240

Channel

Fig. 5.IVe~ gamma-ray pulse-height spectrum for

pulse-height spectrum for the 1.27-MeV gamma rayfrom 2~a for a bare source and for the situationwhere a 0.32-mm-thick iron absorber was placedbetween the source and the detector. With the ironabsorber in place, the ratio R (number of counts inthe tail extending from the full energy peak to zeroenergy to the total number of counts in the tail pluspeak) increased over the same ratio for the baresource case. The effect results from two phenomena.(1) The gamma rays were degraded in energy byscattering in the sample and were added to thenumber of counts occurring in the tail, and (2) thenumber of counts in the peak was decreased by theexpected amount as a result of absorption andscattering.

Gamma - Ray Energy (MeV )I 2 3 4 5 6 71 , ! I I ,

A Chromium 1

lo’~0 40 80 I20 160 200 240

Channel

Fig. 6.Net gamma-ray pulse-height spectrum forchromium.

Gamma - Ray Energy ( MeV ),.40 I 2345678

~

IL .1Nickel

103 ●

mE .,.: .0 .●

102 I “*” . ..0

. ..k

I

““”++

10’ , , I , , , , ! , 1 10 40 80 120 160 200 240 280

Channel

Fig. 7.Net gamma-ray pulse-height spectrum for nickel.

To simulate the geometry of the samples actuallyused to obtain the experimental data, responsemeasurements were made for situations wheresources were placed inside a thin-walled ironcylinder, between two thin iron disks, as well asisolated sources. The ratio of counts in the tail divid-ed by counts in the tail plus counts in the peak (aftercorrection for gamma-ray absorption) was deter-mined for these source geometries.

An estimate of the sample geometry effect wasmade to extend these measurements to othersamples. Details of this calculation are described in

Gamma - Ray Energy (MeV ),.40 I 2 3 4 5 6 78

j

Copper

103.

mE .3

s

102

i

1-.-110’ ,

0 40 80 120 160 200 240 280Channel

Fig. 8.Net gamma-ray pulse-height spectrum for copper.

3

Gamma. Roy Energy (MeV)~4 o I 2 3 4 5 6 7

I I

Molybdenum

IO’ .

IllE ●3

(s

102: .

7

10’1 I t 1 1 I I I 4 I ,1 10 40 80 120 160 200 240

Channel

Fig. 9.Net gamma-ray pulse-heightmolybdenum.

Gam2ma-Roy En:rgy40 I

10 ~ I I I

103–

Inz:u

102-

spectrum for

(MeV)

~

Ntobium

! +-’_1-o-1

I I-.-II

10’ I I I I I Im1 I

o 40 80 120 160

Channel

Fig. 10.

Net gamma-ray pulse-height spectrum forniobium.

Gamma - Ray Energy ( MeV)

I TontalumL103 :

In

c3G

●

102–

m

,.40 I 2 3 4

I -110’ I I I I I I I I J

o 40 80 [20 160

Channel

Fig. 11.Net gamma-ray pulse-height spectrum for tan-talum.

the Appendix and indicate that the ratio R for an ar-bitrary sample can be related to the measured ratiofor the iron standard by

%a = ‘st

[,;%.%,2J

[ 1-(n~tuJ2) “l-eHere, R~ is the ratio of counts in the tail divided bytotal counts in the tail plus peak observed with a sam-ple, a= is the scattering cross section of the sample,and n= is the areal density of the sample. Theequivalent quantities for the standard (here taken asiron) are Rd, ad, and nd. By this method the ratio Rwas obtained for all of the samples used in the ex-periment.

Finally, the gamma-ray line shapes obtained fromthe detector were described in terms of (1) a Gaus-sian distribution around the peak energy with (2) arelatively flat tail extending to zero energy. The ratioR was parametrized over the 0.2-to 10-MeV gamma-ray energy range. This information, with the absoluteefficiency of the detector, was incorporated intoNIBL, which derived the desired photon spectra by

.

‘,

4

“

successively stripping NaI (Tl ) response functionsfrom the net NaI(Tl) ,spectra.

C. Neutron Flux Measurements

During this experiment, several separatemeasurements were made of the absolute neutron in-tensity. Two proton-recoil telescopes with differentgeometrical arrangements were used. Both countersused silicon and NaI(Tl ) detectors in a coincidencearrangement to distinguish the recoil proton pulsesfrom other pulses. A large resolving time ( w5- to 8-K) was used in the coincidence circuit to ensure thatno proton pulses were lost due to time jitter. Further,electronic hvetime (greater than 99~0) was measuredby connecting a 60-Hz puleer to the test input of bothpreamplifiers and computing the ratio of the numberof these pulses that appeared in the spectra to the inumber of times the puleer fired.

The neutron intensity was measured as a functionof the gas cell pressure and beam current over thesmall premwe range used in these experiments. Allof the measurements agreed to within 5% with theneutron intensity calculations, which were made ue-ing appropriate cross sections for the 2H(t,n)4He

Gamma-Ray Energy ( MeV),040 I 2 3 4 5

Platinum

103–

Wz:0

102-

lo’o~Chaonel

Fig. 12.Net gamma-ray pulse-height spectrum forplatinum.

Gamma-Ray Energy (MeV)

’04-

Io:l

Channel

Fi~. 13.Net gamma-ray pulse-%eight spectrum for 23SU,

Gamma-Ray Energy ( MeV),.40 I 2 3 4 5

I I I I -1

lo’~o 40 80 120 160

Channel

Fig. 14.Net gamma-ray pulse-height spectrum for 239Pu.

Gamma Ray Energy (MeV)~40 I 234 5678

a t

. .._Id ., , t ,0

,40 80

1--1120 160 203 240 280Channel

Fig. 15.Pulse-height spectrum for iron (time-independentbackground was subtracted) and a corresponding no-sample pulse-height spectrum.

I I I I I I800 - Carbon

(4.4 Mev )

600 -

400 -

II

““m10’–

@lE3G

10’–

24 NO

[1

137~,

(2.75, I 37 MeV ) ( 0.662 MaV )

H I HI D. Multiple Scattering

Fig. 16.Gamma-ray pulse-height spectra for monoenergeticgamma rays. The 4.4-Me V line was obtained from

t

AE spectrum

●

●

●

IA ●E 300 -

●

28

●

200– ● .

100 -8

+*”= , , “o}

o20 60 00 140 160

L E spectrum 4

Channel

Fig. 18.Puhe-height spectra for the proton recoil telescopefor both AE (silicon) and ~NaI(Tl)~ detectors.Squares represent background counts with thepolyethylene radiator removed. .

low-energy (0.5 -MeV) part of thegamma-rayspec-trum and was decreased linearly to zero at 8 MeV.This rather arbitrary procedure introduces only smalluncertainties because the multiple scattering effect isonly about 4% or less.

For the fissionable elements, the correction wasapplied to the entixe spectrum because most of thegamma rays are associated with fission fragmentsand the spectrum shape is not altered by multiplescattering.

E. Cross-Section Calculations

Differential cross sections were calculated forgamma-ray production as a function of gamma-rayenergy by

NT X d2U(E7,0) =

FXE(E7)XN ‘

(1)

where N7 is the number of gamma rays in an energyinterval, d2 is the harmonic mean of the square of thedistance from the neutron source to the sample, F isthe time-integrated neutron flux, c(E,) is theefficiency of the gamma-ray spectrometer for

1

gamma-ray energy EY, and N is the number ofsample atoms. Corrections were made for multiplescattering of neutrons in the sample (

TABLE I

DIFFIXENTIALGAMMA-RAY PRODUCTIONCROSS SECTIONS AS A FUNCTION OF GAMMA-RAY ENERGY

ALUMINUM

128°

EstCross Uncer-iection tainty&A?Ql!!!M@2.3 0.63.2 0.60.61 0.360.0 0.35

3.2 0.53.4 0.56,0 0.7

CNROMIUFl

1200

IRONElement + MAGNESIUM

goo

EstCross Uncer-;ectiontainty

k!!2f&Q@?.&l5.1 0.62.8 0.41.7 0.30.56 0.211.5 0.22.7 0.32.0 0.3

1280

EstCross Uncer-ection taintymb/sr) (mb/sPj

7.2 1.03.7 0.81.8 0.50.36 0.46

2.0 0.52.3 0.52.0 0.5

goo

EstCross Uncer-ection taintymb/sn) (mb/srj

6.2 0.612.1 1.38.3 0.95.0 0.5

15.0 1.534,5 3.511.8 1.2

120”

EstCross Uncer-;ectiontainty

J!WQ4Z!W!?Q8.1 1.3

10.2 1.24.2 0.31.8 0.7

15.7 2.043.4 4.612.8 1.5

6.9 0.811.0 1.423.3 2.413.3 1.44.9 0.63.0 0.54.0 0.55.4 0.64.7 0.63.6 0.4

Angie +

EnergyInterval(MeV)

0.3 - 0.40.4 - 0.50.5 - 0.60,6 - 0.70.7 - 0.80.8 - 0.90.9 - 100

1.0 - 1.11.1 - 1.21.2 - 1.31.3 - 1.41.4 - 1.51.5 - 1.61.6 - 1.71.7 - 1.81.8 - 1.91.9 - 2.0

Cross Uncer-iectiontainty

!!wQ (*J=;6.5 0.99.8 1.1.9.1 1.09.8 1.1

10.4 1.110,5 1.112.2 1.3

5.0 0.66.1 0.6

11.6 10229.5 3,033.7 3.412.4 1.32.8 0.43*4 0.42.2 0.32.3 0.3

1.9 0.32.8 0.35.5 0.616.5 1.78.3 0.92.2 0.32.3 0.33.6 0.43.6 0.42.0 0.2

1.5 0.52.3 0.56.2 0.817.9 1.98.5 1.01.3 0.41.8 0.43.1 0.53.4 0.52.5 0.4

4.1 0.51.2 0.31.5 0.31,3 0.31.2 0.31.4 0.33.1 0.47.1 0.s6.5 0.72.9 0.4

6.5 0.79,7 1.118.6 1.810.0 1.04.1 0.42.7 0.33.6 0044.5 0054.3 0.53.1 0.3

2.0 - 2.12.1 - 2.22.2 - 2.32.3 - 2.42.4 - 2.52.5 - 2.62.6 - 2.72.7 - 2.82.S - 2.92.9 - 3.0

1.1 0.21.0 0.20.97 0.150.98 0.141.3 0.21.4 0.21.7 0.21.9 0.21.7 0.21.1 . 0.1

1.1 0.30.75 0.270.49 0.251.1 0.30.93 0.241.4 0.31.82.3 ;::2.0 0.31.2 0.3

2.4 0.34.7 0.56.0 0.73.6 0.42.3 0.31.7 0.31.3 0.21.4 0.21.9 0.33.7 0.4

3.9 0.52.4 0.3L.4 0.20.96 0.180.62 0.160.53 0.160.78 0.170.90 0.180.88 0.181.2 0.2

2.6 0.42.2 0.32.3 0.32.3 0.31.7 0.31.8 0.21.6 0.21.7 0.21.6 0.21.7 0.2

2.3 0.32.3 0.32.3 0.31.8 0.31.3 0.21.6 0.21.8 0.21.5 0.21.7 0.21.4 0.2

2.9 0.33.0 0.32.3 0.32.2 0.32.7 0.33.2 0.42.7 0.32.1 0.21.9 0.21.9 0.2

1.8 0.22.0 0.22.0 0.21.9 0.21.9 0.21.9 0.21.8 0.21.7 0.21.4 0.21.4 0.2

3.2 0.43.2 0.42.4 0.32.5 0.42.7 0.4 -3.6 0.5

0.4H 0.32.0 0.32.1 0.3

2.0 0.32.2 0.32.5 0.32.3 0.32.2 0.32.3 0.32.2 0.32.0 0.31.7 0.31.7 0,3

3.0 - 3.13.1 - 3.23.2 - 3.33.3 - 3.43.4 - 3.53.5 - 3.63.6 - 3.73.7 - 3.83.8 - 3.93.9 - 4.0

4.0 - 4.54.5 - 5.05.0 - 5.55.5 - 6.06.0 - 6.56.5 - 7.07.0 - 7.57.5 - 8.08.0 - 8.58.5 - 9.0

0.97 0.140.79 0.120.67 0.110.54 0.100.75 0.120.69 0.110.92 0.131.34 (1.21.5 LJ.21.4 6.2

1.0 0.21.1 0.20.67 0.210.64 0.201.1 0.20.5 0.210.95 0.221.0 0.21.s 0.31.4 0.3

1.3 (,.270.71 (!.230.51 (:.210.56 Q.210.56 (j.240.50 0.250.59 0.240.64 0.220.41 0.130.61 0.14

1.3 0.270.71 0.230.51 0.210.56 0.210.56 0.240.50 0.2s0.59 0.240.64 0.270.41 0.130.61 0.14

0.94 0.200.90 0.200.75 0.190.73 0.190.56 0.210.49 0.240.56 0.230.59 0.160.32 0.110.45 0.13

1.4 0.21.4 0.21.2 0.21.3 0.21.0 0.20.87 0.240.94 0.250.91 0,180.91 0.180.71 0.16

1.2 0.21.0 0.20.99 0.140.99 0.150.98 0.170.98 0.180.88 0.160.79 0.150.69 0.130.60 0.12

1.4 0.21.2 0.21.2 0.21.1 0.21.2 0.21.1 0.21.0 0.20.90 0.170.79 0.180.64 0.14

-.

f‘.

#

TABLE”I (cent)

COPPER MOLYBDENUMElement + NICKEL NIOBIUM

1200goo

EstCross Uncer-ection taintymb/sr) (mb/sr)——

--- ---

-- ---

20..3 2,129.4 3.052.5 5.342.9 4.322.6 2.3

1200

EstCross Uncer-,ectiontaintymb/sr) (mb/sr’—-22.1 2.527.6 3.624.5 2.940.6 4.563.4 6.746.3 4.825.5 2.7

Angle + 12 o“

EstCross Uncer-;ectiontaintymb/sr) (mb/sr)

12.1 1.313.2 1.43.7 0.52.5 0045.0 0.54.6 0.58.2 0.8

9.1 0.912.5 1.215.4 1.518.8 1.916.1 1.6

7.5 0.84.5 0.44.6 0.54.2 0.52.9 0.3

120’J

EstCross Uncer-,ectiontainty

!!!zSd (fijsr;

22.0 2.415,8 1.710.1 1.110.1 1.16.7 0.7

10.6 1.021.0 2.1

EnergyInterval(MeV)

Cross Uncer-ection taintymb/sr) (mb/sr)——29.4 3.230,5 3.317.6 1.912.2 1.516.7 1.814.9 1.725.2 2.6

0.3 - 0.40.4 - 0.50.5 - 0.60.6 - 0.70,7 - 0.80.8 - 0.90.9 - 1.0

1.0 - 1.11.1 - 1.21.2 - 1.31.3 - 1.41.4 - 1.51.5 - 1.61.6 - 1.71.7 - 1.81.8 - 1.91.9 - 2.0

16.8 1.723.9 2.415.8 1.613.3 .1.49.9 1.07.3 0.85.9 0.75.0 0.55.6 0064.5 00s

20.7 2.116.6 1.711.3 1.2100’5 1.113.3 1.314.1 1.49.8 1007.7 0.86.3 0.75;9 0.6

23.8 2.61806 2.012.2 1.311.6 1.315.4 1.714.7 1.69.7 1.17.4 0.86.4 0.7601 0.7

14.4 1..611.6 1.37.9 1.09.7 1.29.4 1.1801 1“;07.2 0.9U.4 0.76.0 0.86.2 0.8

2.0 - 2.12.1 - 2.22.2 - 2.32.3 - 2.42.4 - 2.52.5 - 2.62.6 - 2.72.7 - 2.82.8 - 2.92.9 - 3.0

3.0 - 3.13.1 - 3.23.2 - 3.33.3 - 3.43.4 - 3.53.5 - 3.63.6 - 3.73.7 - 3.83.8 - 3.93.9 - 4.0

4.0 - 4.54.5 - 5.05.0 - 5.5S*5 - 6.06.o - 6.56.5 - 7.07.0- 7.57.5 - 8.08.0 - 8.58.5 - 9.0

2.4 0.32.4 0.32.1 0.22.2 0.22.2 0.32.1 0.22.3 0.32.2 0,32.3 0.32.b 0.3

3.4 0.43.1 0.42.5 0.32.5 0.32.2 0.32.1 0.31.9 0.21.8 0.21.9 0.21.7 0.2

5.5 0.64.8 0.5Q.3 0.53.9 0.43.8 0.43.2 0.33.0 0.32.8 0.32.7 0.32.2 0.2

5.5 0.74.9 0.64.4 0.64.2 0.53.7 0.53.3 O.b3.0 0.43.0 0.42.6 0.42.3 0.3

2.3 0.31.9 0.32.0 0.31.7 0.31.4 0.31.4 0.31.3 0.31.0 0.21;2 0.21.0 0.2

7.3 0.97.3 0.96.2 0.85.0 0.63.5 0.53.2 0.52.2 0.43.0 0.52.2 0.42.4 0.4

1.6 0.41.3 0.41.7 0.41.5 0.40.45 0.311.1 0.31.2 0.30.68 0.331.3 0.30086 0.32

2.5 0.32.3 0.32.1 0.21.9 0.21.5 0.21.4 0.21.4 0.21.3 0.21.3 0.21.1 0.2

1.7 0.21.6 0.21.6 0.21.6 0.21.5 0.21.3 0.21.4 0.21.3 0.21.3 0.21.1 0.2

2.0 0.22.0 0.21.8 0.21.7 0.21.6 0.21.4 0.21.3 0.21.3 0.21.2 0.21.1 0.1

1.2 0.21.1 0.21.1 0.20.96 0.170.92 0.180.81 0.180.77 0.160.67 0.130.54 0.130.36 0.08

1.2 0.20.95 0.170.81 0.150.78 0.150.64 0.150.59 0.150.40 0.110.29 0.070.15 0.050.13 0.05

0.95 0.140.69 0.110,51 0.100.45 0.090.39 0.090.26 0.090.23 0.070.15 0.050.09 0.030.08 0.03

0.83 0.240.66 0.230.52 0.240.46 0.290.38 0.280.33 0.250.26 0.140.17 00110.14 0.080.13 0.08

0.56 0.330.65 0.280.29 00300.35 00300.33 0.320.30 0.380.30 0.310.12 0.140.14 0.140.13 0.12

.

TABLE I (cent)

Element +

Angle +

EnePgyInterval(MeV)

0.3 - 0.40.4 - 0.s0.5 - 0.60.6 - 0.7

0.7 - 0.80.8 - 0.90.9 - 1.0

1.0 - 1.11.1 - 1.21.2 - 1.31.3 - 1.41.4 - 1.s1.5 - 1.61.6 - 1.7L7 - 1.81.8 - 1.91.9 - 2.0

2.0 - 2.12.1 - 2.22.2 - 2.32.3 - 2.42.4 - 2.52.5 - 2.62.6 2 2.72.7 - 2.82.8 - 2.92.9 - 3.0

3.0 - 3.13.1 - 3.23.2 - 3.33.3 - 3.43.4 - 3.53.5 - 3.63.6 - 3.73.7 - 3.83.8 - 3.93.9 - 4.0

4.0 - 4.54.5 - 5.05.0 - 5.55.5 - 6.06.0 - 6.S6.5 - 7.07.0 - 7.57.5 - 8.08.0 - 8.58.5 - 9.0

TANTALUM

12O’J

EstCross Uncer-;ectiontainty[mb/sr)(mb/sr)— —

63.4 7.471.4 7.731.0 3.716.6 2.4

15.9 2.317.3 2.419.4 2.5

23.3 2.823.1 2.816.6 2.219.0 2.416.9 2.213.9 1.913.4 1.812.0 1.712.4 1.711.5 1*5

10.6 1.411.2 1.59.6 1.38.9 1.27.8 1,16.7 1.06.4 1.06.8 1,05.8 0.95.2 0.9

4.7 0.93.4 0.84.6 0.94.1 0.82.2 0.72.6 0.82.3 0.71.2 0.73.0 0.71.8 0.7

1.2 0.70.77 0.610.40 0.630.60 0.640..59 0.770.84 0.930.37 0.600.19 0.350.27 0.220.30 0.24

PLATINUM

1220

EstCross Uncer-ection taintymb/sr) (mb/sr)——128 13152 1588.5 8.935.6 3.722.4 2.420.0 2.117.6 1.9

20.3 2.219.8 2.116.7 1.816.8 1.816.9 1.8

16.9 1.816.2 1.7

16.2 1.713.8 1.511.3 1.2

10.7 1428.8 1.08.3 0.97.9 0.97.4 0.86.5 O*76.4 0,75.4 0.65.3 0.63.7 0.5

3.1 0.52.6 0.43.1 0.42.3 O.u

1.8 0.31.9 0.31.4 0.31.9 0.41.3 0.31.5 0.3

0.66 0.290.71 0.260.56 0.270.14 0.270.30 0.300.35 0.370.17 0.190.19 0.1s0.09 0.080.08 0.07

URANIUM

120”

EstCross Uncer-ection taintyrnb/sr)Jmb/sr]

201 20217 22161 17130 13111 1193 1078 7.8

63 6.460 6.055 5.548 4.840 4.137 3.734 3.332 3.428 2.825 2.6

21 2.219 2.118 2.015 1.714 1.513 1.312 1.39.9 1.19.2 1.18.6 1.0

6.2 0.95.8 0.85.7 0.85.3 0.84.7 0.73.7 0.73.6 0.64.0 0.74.0 ‘0.72.9 0.7

2.6 0.61.8 0.61.2 0.60.7 0.60.9 0.60.7 0.70.6 0.40.3 0.2

PLUTONIUM

1200

EstCross Uncer-ection taintymb/sr) (mb/sr~

281 29262 27202 2115Q 15126 13102 1181 9.6

70 8.365 8.158 7.348 6.140 4.936 4.531 4.229 3.824 3.121 2.7

20 2.819 2.615 2.214 2.112 2.012 2.010 1.89.5 1.79.7 1.88.0 1.6

5.7 1.44.7 1.48.2 1.64.5 1.34.5 1.42.3 1.34.3 1.32.3 1.33.4 1.33.6 1.3

1.7 1.21.4 1.01.4 1.00.6 0.60.8 0.70.9 0.80.8 0.40.5 0.3

.—

.

“L

10

TABLE 11

DIFFERENTIAL GAMMA-RAY PRODUCTION CROSSSECTIONS FOR PROM3NENT GAMMA RAYS

Gamma-Ray Energy Cross SectionElement Angle(MeV) (mblsr)

Carbon 4.4

Magnesium 1.37

1.81

2.8

Aluminum 0.84

1.01

1.8

2.2

3.0

Chromium 1.33 + 1.44iron 0.845

1.24

456490

125

122

90122

90122

90122122

122122122

123122

90122

90

21.3 * 2.815.0 + 2.011.6 *1.516.1 *2.130.3 f 3.327.2 * 3.0

8.3 & 1.28.2 ~ 1.2

4.2 * 0.76.2 + l.o

5.4 * 1.1

10.6 + 2.1

16.7 k 2.513.5 *2.O

8.4 * 1.3

76.7 k 9.265.6 * 7.o53.2 *5.634.0 * 4.127.8 * 3.3

APPENDIX

MODIFICATION OF RESPONSE FUNCTIONSDUE TO PHOTON SCATTERING

Neutron-induced gamma-ray production croee-section measurements usually involve unfolding orstripping of complex pulse-height spectra. Responsefunctions used in the unfolding process are obtainedfrom monoenergetic gamma-ray sources and consistprimarily of a Gaussian full-energy peak and arelatively flat tail due to Compton collisions in thedetector.

This Appendix shows that for samples of moderatesize, this tail can be significantly larger than thatmeasured with the usual gamma-ray sources.

For simplicity, the sample ia taken to be a cubewith aides t in length and n atoms/cm3, G ~monoenergetic gamma rays are produced uniformlythrough the sample, u, is the gamma-ray scatteringcross section, and the detector area is AA and is

located a distance R from the sample. Also, nut istaken to be small.

Assuming that (1) (1 -AA/47rR2) = 1, (2) efficiencyfor scattered gamma rays ia the same as the directgamma rays, and (3) absorption cross section forscattered gamma rays is the same as for direct gam-ma rays, the ratio of scattered gamma-ray counts tocounts from direct gamma rays is (errors caused byassumptions 2 and 3 tend to cancel)

( –na~t12l-e ).For most samples, this is a modest increase in

counts (-13% for a 6.4-mm-thick sample of iron and1.27-MeV gamma rays), but for detectors whose baresource response functions have small tails compared

11

to full-energy peaks, the relative magnitude of thetail can be increased significantly (Fig. 3 shows anincrease of about 70Yo).

In complex gamma-ray spectra that have been un-folded with bare source response functions, this effectwould appear to be an extra continuum of gammarays.

REFERENCES

1. G. Hansen, R. K. Smith, Los Alamos ScientificLaboratory, and G. G. Simons, University of Wyom-ing, personal communication, May 1974.

2. J. C. Hopkins and G. Breit, “The lH(n,n)lHScattering Observable Required for High-PrecisionFast-Neutron Measurements,” Nucl. Data Tables A9,137 (1971).

3. E. D. Cashwell, ]. R. Neergaard, W. M. Taylor,and G. D. Turner, “MCN: A Neutron Monte CarloCode,” Los Alamos Scientific Laboratory report LA-4751 (January 1972).

EE:209(60)

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