Penetration through Shielding Materials of SecondaryNeutrons and Phtons Generated by 52-MeV Protons
Y. Uwamino*, T. Nakamura** and K. Shin**** National Institute of Radiological Sciences** Institute for Nuclear Study, University of Tokyo*** Department of Nuclear Engineering, Kyoto University
Attenuation of neutrons and photons transmitted through graphite, iro:rt, water and ordinary concrete assembl.ies were studied.
Energy sp~ctra of neutrons (E ~ 2 MeV) and photons (E ~ 0.4 MeV)
were meas¥red using an NE-213 organic scintillation detector with ann-y discr.imination technique, and thermal and fast neutron flux
distributions in an assembly were measured with gold and iron actiSource neutrons and photons were provation foils, respectively.
duced by 52-MeV proton bombardment of a 21. 4-mm-thick graphite tarThe distributions of the light
get place4 in front of the assembly.
output frpm the scintillator were unfolded by the revised FERDO codeusing neutron and photon response functions calculated by the Monte
These experimental results were used as benchmark data
Carlo codes.
on neutron and photon penetration by neutrons of energy above 15
Multigroup Monte Carlo, one-dimensiona l ANISN and two-dimenMeV.
sional DOT-3.5 transport calculations were performed with the DLC58/HELLO .group cross sections to compare with the measurement andto evaluate .the cross sections. Source neutrons of energy below
the lower limit of the measurement (2 MeV) were estimated by theevaporation model.
Figure 1 shows the absolute comparison of measured and calculated forward neutron spectra transmitted through ordinary concrete
shield, as an examplel). The results of the ANISN calculation ofneutrons in slab geometry and the three-dimension al .Monte Carlocalculation agreed with the experimental values. The attenuationsof neutron fluxes integrated above 2 MeV are shown in Fig. 2. The
agreement·of ANISN and Monte Carlo calculations is well within theaccuracy .of 7% in the measured attenuation coefficients for graphite, iron and water, and less than 10% for concrete. As shown inFig. 3, the DOT-3.5 calculation .. in cylindrical geometry is in good
agreement.with thermal neutron flux distribution in a 44.5-cm~thickFig. 4 showsgraphite assembly measured with gold activation foils.
the attenuation profile of the photon flux integrated above 0.4 MeV.
The ANISN calculation gave more than 20% overestimation of thephoton attenuation coefficients in the case of deep penetration
through the medium for which the photon mean-free-path is shorter
than that of neutrons, such as in iron and concrete. The secondary
photons produced by the neutron-nucleus reactions are dominant compared with the primary photons, but otherwise the ANISN calculations
gave good .results. As an example, Fig. 5 shows the absolute comparison of measured and calculated forward photon spectra transmitted through concrete. This difference may ne explained by that thephotons produced by neutron-nucleus nonelastic collisions of energies of higher than 14.9 MeV .are neglected in DLC-58, and that the-61-

photons scattered by the walls and theceiling make a noticeable contribution
compared with strongly attenuated photons
through these thick shields.
'c:8~

Reference':'1) Y. Uwamino, T. Nakamura and K. Shin
Nucl. Sci. Eng., 80, 360 (1982).

5> 10'9~2.sX=>"'c:00.cc..

Photon energy (MeV)

Fig. 5. Comparisons in absolute value of measured andcalculated forward photon spectra transmitted through ordi-nary concrete assemblies.
10-2'7c:000.
---::;; 10'3E.

>.,.~ w-4
ciA!:!::

Neutron energy (MeV)X=>

Fig. 1. Comparisons of absolute values of measured and"'c: 10'5calculated forward neutron spectra transmitted through ordinary concrete assemblies.

00.c0.

-;;;

0r------.---,------,--T----:c:
000.

"'!

f-w-60Material thickness (g·cm-2)

f:'.

Measured and calculated attenuation profiles ofFig.
the photon fluxes integrated above 0.4 MeV .

·~ 1Q-3.s>~"'A 10-4

Fig. 3!:!::
X=>"'c: 10'5£;ilc:"§o Measured by Au Activation Foil

0f-10"60• Colculated by .DOT-3.5 Code1000

Material thickness (g·cm-2)

Fig.2. Measured and calculated attenuation profiles of_ theneutron fluxes integrated above 2 MeV. The calculauons
shown here were obtained by the Monte Carlo code.

0102030

Deeth in 44 .5-an--thlck Groch! te, Clll

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