抄録
The transmission factor of annihilation γA rays (511 ke V) for radiation shielding materials has been estimated by means of the Monte Carlo simulation based on three kinds of geometries of (1) a point isotropic source in infinite thick material, (2) a point isotropic source in finite thick material and (3) vertical incident to finite thick material. The present results show that the factor for geometry (1) is the largest, that for geometry (2) is next and that of the geometry (3) is the lowest. We have also found the cases in which the factor for geometry (1) is 2-3 times larger than the factors for geometries (2) and (3).
The transmission factors for main γA-ray emitting nuclides, given in “Manual of Practical Shield Calculation of Radiation Facilities (2000)”, are available only for the geometry (1). The present work indicates that the use of these values the calculation for actual shield geometries often causes the overestimate of effective doses. The transmission factor data for the geometries (2) and (3) are clearly necessary for more reliable shield calculations.
