Optimum arrangement to minimize total dose rate of iron-polyethylene shielding system.

Abstract

The shielding experiments using iron-polyethylene slab shields with a 252Cf neutron source were carried out to find out an optimum arrangement to minimize the total dose rate; that is composed of neutron and secondary γ-ray dose rates. The total thickness of the iron slabs was fixed at 32 cm, while a variety of thickness and location of a polyethylene slab in the iron slabs were employed as a parameter. The minimum dose point (i.e. optimum shielding arrangement) was observed when the polyethylene slab was located at approximately 20 cm depth from the source side in the arrangements. The ratio of the minimum dose rate obtained for the optimum arrangement to the maximum for the worst arrangement became 1/1.3 for the polyethylene slab of 1-cm-thick, 1/2.0 for 3-cm-thick, 1/2.9 for 6-cm-thick, 1/3.9 for 10-cm-thick and 1/3.6 for 14-cm-thick. The appearance of the optimum arrangement for the total dose rates, and changing profiles of the secondary γ-ray as well as the neutron dose rates were reproduced for the typical two cases of the polyethylene slab thickness by the Monte Carlo calculations with the splitting technique.