Design of labyrinth systems for radiation shielding

The shielding labyrinths for gamma-ray irradiation should be designed corresponding to respective objectives of use, such as research, medical treatment, industry and agriculture. However it is relatively difficult to estimate the radiation dose in labyrinth spaces at the design stage, therefore it is desirable to carry out the design and construction of labyrinths referring to the actual examples of existing facilities. Thereupon, it is necessary to devise more rational and practical method of design of labyrinths to estimate the scattering dose and leaking dose in shielding labyrinths beforehand, and to rationalize the design and construction of labyrinths. This study aimed at establishing the shield design method for the rational and safe labyrinths for irradiation by carrying out various experiments and obtaining the required data, and contributing to the prevention of radiation injuries. The model labyrinths of ordinary concrete was made, and the distributions of spatial dose and energy in it were measured with Co-60 source. The relation between the effective atomic numbers of various shielding materials and backward scattering coefficients was determined. The effect of reducing backward scattering beam by covering the plane concrete surface with lead was determined. The experimental methods and the results are reported. (Kako, I.)