Shun-ichi Miyasaka

Dose Buildup Factors of Multi-Layer Slabs for a Point Isotropic Source

Dose buildup factors for multi-layer slabs composed of lead and graphite were obtained experimentally for a point isotropic source of 60Co and 137Cs. The experimental results are compared with those calculated by the Monte Carlo method, and show a good agreement. The buildup factors for the second material behind the first increase — or decrease — very markedly for heavy-light — and light-heavy — layers. From these experimental results, it would be possible to assume that the dose buildup factor for the second material of a double layer slab is composed of two parts, namely asymptotic and transient. The transient part is that which increases or decreases very rapidly within about 1 mean free path from the interface of the first and second layers. The asymptotic part increases proportionally with the buildup factor for the second material. The rise or fall of the buildup factor in the second material can be explained from the change of the spectra in the second material. From the experimental results, the ...

Neutron and Gamma-Ray Penetrations in Thick Iron

Measurements of neutron and gamma-ray penetrations in an iron shield were performed up to a 60-cm depth in a tightly coupled source shield configuration with the fast-neutron reactor YAYOI as a source. Rates of neutron reactions and gamma-ray dose rates in the iron shield were obtained using activation foils and thermoluminescent dosimeters. Analyses of the experiments were made by using the DOT-III code with coupled neutron and gamma-ray cross sections from ENDF/B-IV and POPOP4 libraries. To obtain the source condition for the iron shield analyses, the calculated spectrum was adjusted to the measured reaction rates at the reactor shield boundary. The calculated neutron and gamma-ray distributions in the iron shield show fairly good agreement with the experiments. The effect of difference in Bondarenko-type self-shielding factors on the analyses of the iron shield is also shown.

Albedo Component of Gamma-Ray Streaming through Straight Cylindrical Ducts

An experimental study was performed to investigate the effect of γ-ray streaming through cylindrical steel and lead ducts having various lengths and radii. In the experiment, 60Co and 137Cs point sources, and small sized detector (pulse dosimeter with plastic scintillator) was adopted, source and detector being located at the centers of opposite duct mouths. The albedo-to-direct component ratio is about 30% for steel ducts and 10% for lead at γ-ray energies of 1.25 and 0.661 MeV, with L/R 0~10. The measured results were compared with those calculated by the Monte Carlo method; they showed a good agreement. Consequently, the prediction of doses for straight cylindrical ducts having various length-to-radius ratios can be made by the procedures based on the Monte Carlo calculations.

GAMMA-RAY LEAKAGE THROUGH A SLIT IN LEAD SHIELD. I.

In continuation of a series ot mockup tests for the first Japanese nuclear ship, reactor γ-ray leakage through a double-bend two-dimensiond passage in a leqd slab was experimentally studied. This zig-zag slit channel is recognized to be an effective device against γ-ray leakqge at shield seams. Such leakage may occur through straight passages with normally incident γ-rays, or else with oblique incidence, in the form of streaming.In the case of zig-zag channel, it should be noted that there exist certain incident angles at which the shielding effect is morkedly impaired. The components of penetration calculated by ray-analysis method have been compared with experimental results. The existence of a slit in a lead slab increases scattered γ-rays, which are localized near the shield surface, but which spread widely with increasing distance from wall.