TRANSMISSION EXPERIMENT OF HIGH ENERGY NEUTRONS
Kagetorno Miyahara , Kazuo Shin
Department of Nuclear Engineering, Kyoto University
Yoshida, Sakyo-ku, Kyoto 606, Japan
andYoshitorno Uwarnino
Institute of Nuclear Study, University of Tokyo
Midori-cho, Tanashi-shi, Tokyo 188, JapanandHideaki Sakai
Department of Physics, University of Tokyo
Hongo, Bunkyo-ku, Tokyo 113, Japan
andKen-ichi Torninaga
Research Center of Nuclear Physics, Osaka University
Mihogaoka, Ibaraki-shi, Osaka 567, Japan
andShigeo Nurnata
Shimizu Construction Co.,LTD.
Etchujirna, Koto-ku, Tokyo 135, Japanlead, graphite and concrete shields.
White neutrons generated by bombardmentof 65 MeV protons on a thick copper
target are utilized this time for theThe energy spectra of transmitted
neutrons through shield systems of iron,
lead, graphite and concrete wereobtained by unfolding the pulse height
thedistributions measured behindshields with an NE-213 scintillator.
These measured spectra were comparedwith calculated spectra by using MORSE
code

twowithsetsofneutron

Experimental Method
The experiment was carried out at theneutroncrosssectiontoaredatadiameter

aboverarevery

15 MeV, the accuracy of the shielding
design made with the above crosssections is not well known.
ourearliertransmitted

neutronInmaterials

severalworks,4,5)

spectraweremeasured

concrete

AVF

thecollimator

neutrons

wereshieldsystemthebehindinch(7.6-crn)

diameterbymeasuredby

3-incha3-height

NE-213 scintillator with an aid of apulse-shape discrimination circuit. The
background data were obtained in the same
experimental condition except thecollimator was closed by an iron plug.
Obtained pulse-height spectra wereunfolded to neutron energy spectra byFERDO method?) with measured response
data8l.

throughtheenergy range up to 30 MeV and the DLC-87
data were found to give good agreementwith the measured data. In the present

5-7.5cmi<'-----378crn----->~- tiron-lined

Transmitted

just

thein

inof 50-ern thickness. The experimental
setup is depicted in Fig.1. The iron,graphite and concrete shields werelead,used in the experiment. Table 1 lists thedimensions of the shields.

thebenchmark

coursecyclotron facility of Osaka University. A
1- ern thick (i.e. proton stopping range)copper target was irradiated by 65 MeV
protons and generated neutrons in theforward direction were pulled out to an
7. 5-crn
experimental room through aexperiments

transmission

utilizedbeneutron

monoenergy

The shield design of medium-energy
accelerators up to a few hundreds MeV isbeing rnadel,2) based on the DLC-87Hilo3) rnultigroup cross section data.
cansection

cross

thecross-section

Introduction

Sinceandsource,

data of DLC-87 Hilo and those released byLittle are benchrnarked.6)

data, DLC-87 Hilo and those released
These data sets werefrom LANL
benchrnarked by this comparison.

which

iron,

for

madeweremeasurements

work,

Abstract-><-50 ->~

Table 1 Dimensions of shield systems

Cu target

Material.. I I~1/\._~;~~~Vn ~--.~·.. :.Concrete '--'.

·------ ~2D., .·. :·""'·· .

Height(ern)

Iron

40

40

20,40,50,60

Lead

40

40

10,20,30

Graphite

50

40

30,60,90

Concrete

40

40

10,50,100

Collimator

Paraffin
Fig.

Width(ern)I

1 Experimental arrangement.

-330-Thickness(ern)in both of the measured and calculated
data are due to poor s t a t i s t i c s anderrors in response data.
It was revealed by tests on crosssection data that nonelastic crosssections used in the DLC-87 were in agood agreement with experimental values.
total cross sections, the data
But forin the DLC-87 at 15-25 MeV were several
percent smaller than experimental values.
aboveThis is the reason for theoverestimation of the transmitted
spectra.
large
gives
MORSE/LANL
The
overprediction to the measured data as
the shield becomes thicker. This isprobably caused by the t r a n s p o r t
approximation adopted by the LANL datalibrary in processing the pointwise crosssections to the ~ultigroup form.
To check this point, the LANL data set
was applied to the analysis of ascattering experiment of 252cf fission
neutrons. The MORSE/LANL calculation gave
good agreement with measured data atangles other than 0°. But at 0°, i toverestimated experimental values. The
similar calculation with MORSE/DLC-87
gave good agreement with the measured
ones at the entire directions. The bothDLC-87 and LANL data sets were based onthe same pointwise cross sections fromthe ENDF/B-IV in the energy range below
15 MeV. The disagreement between the two
calculations should be due to thedifferent model used by the two libraries
in the multigroup processing.
Fig.3 shows corresponding results forthe lead shield. There is no LANL crosssection data for lead. The comparison isMORSE/DLC-87
thewithonly
madeCalculational Method
The neutron transport in the shieldsystem was calculated by the MORSE codewith the DLC-87 Hilo and the data
developed at LANL6l, in a geometricalmodel which closely simulated theexperimental setup.
P 5 Legendre
The DLC-87 uses
expansion at energies above 15 MeV andP 3 Legendre expansion at energies below
15 MeV. The data are based on the intranuclear-cascade-evapolat ion model fornonelastic scattering and the opticalmodel for elastic scattering. The LANL
data use P 3 Legendre expansion at allenergies. The data were calculated with
the GNASH code based on the preequilibrium model.
The source spectrum measured without
the shield system was utilized in thecalculation.
Results and Discussion
Fig .. 2shows

comparisonofmeasuredand calculated iron transmitted neutron
spectra. The measured spectra are well
reproduced by the DLC-87 data except foroverestimation
about a factor of fiveby the calculation in the energy range
from 15 MeV to 25 MeV. Fluctuations seen

HORSE/OLC-87

MORSE/LANL

20cm

10- 9 ~-------------------------------=

z0r-t o-t20:z(L1--a:0'-~10-too_'>w::;::'N

Gla-tt

50C3'X:::J_Jz0a:

LL[Q-t2EXPER£MENT:za:

MORSE/OLC-87

01-::J1--:zl o-lllw:z1o-t3

:::Jw

Fig.

Fig.

2 Transmitted neutron spectra throughthe --frOii Shields.

-331-3 Transmitted neutron spectra
the lead nhields.

throughcalculation. The disagreement between
the experiment and the calculation isvery large at energies above 15 MeV.
In making up the DLc~87 lead crosssection data set, they omitted theelastic scattering at energies above 15MeV. Since the angular distribution ofelastic scattering is very forward
peaked, they assumed that the elastic
scattering did not contribute to neutron
attenuation and could be omitted.
However this is not true in particularwhen the neutron transmission to theforward direction is considered. The
cross sections of elastic scattering
occupy almost about the half of thetotal cross sections. More over,nonelastic cross sections of lead above
15
MeV
areseveral-percentunderestimated. The overestimation of
the lead transmitted spectra by theMORSE/DLC-87 calculation was caused bythesereasons.
Fig.4 shows r e s u l t s of thecomparison between the experiment andthe MORSE/DLC-87 calculation for thegraphite shield. The agreement between
the two sets of data is quite well
except the calculation gives slight
lower values below 10 MeV.
The comparison of the concrete
transmitted neutron spectra is shown inFig.S. The MORSE/DLC-87 calculation
fairly well reproduces the measured
data. Again the MORSE/LANL calculation
gives overestimation to the measured
data for the thicker shields.

z0f--~lo-LO......

Q_>

w

:4:

......

~to-ll......

X:::::l_.J

1.!...1 0-12z0a:f--::Jw

zl o-13

Fig. 5 Transmitted neutron spectra throUghthe concrete shields.

Conclusion::;:The benchmark test made based on themeasured transmission spectra revealed
that the calculation by the DLC-87 .crosssection data gave well agreement with theexperiment for the graphite and concrete
shields, but partly gave overestimation
at energies 15-25 MeV for the ironshield,andgave
very
large
overestimation above 15 MeV for the leadshield •As for the LANL multigroup data, thetransport approximation is not adequate.

.......

TheGl0- 11

overprediction to the measured spectra atthe thicker shields •EXPERIMENTzDMCJRSE/DLC-87f--Da:to-1oo_.......

>

L1JN.......

calculation

resultedinthelarge

ReferencesX1) R. G. Alsmiller, Jr. and J. Barish,Med. Phys.,!, 51 (1974).
2) W. K. Hagan et al.,Nucl. Sci. and Eng.,~§_, 272 (1988).
3) R. G. Alsmiller, Jr. and J. Bar~sh,
Nucl. Sci. and Eng., §_Q, 448 (1982).
4) K. Shin et al.,Nucl. Sci. and Eng., 2.!• 294 ( 1979).
5) Y. Uwamino et al.,Nucl. Sci. and Eng., §_Q, 360 (1982).
6) R. c. Little et al.,Los Alamos National Laboratory,
LA-UR-88-2874 (1988).
7) K. Shin et al.,Nu c 1 • T e c h no 1 • , ~l· 7 8 ( 1 9 8 1 ) •8) K. Shin et al.,prepared for publication.

::::l_.JLLl 0 -12z

Da:f-::::lL1Jzl o-13

Fig. 4 Transmitted neutron spectra throughthe graphite shields.

-332-