β線被曝の場合の表層部線量当量の放射線管理実務の観点からの評価法とその限度-モンテ・カルロ計算を用いて-

概要

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A practical method for assessing ‘shallow dose equivalent’ for beta-rays, as secondary limits of protection standards, has been studied using Monte Carlo method. Dose distribution at various depths within a surface layer of human body were estimated in the cases of irradiation from 3H, 14C, 147Pm, 133Xe, 131I, 85Kr, 204Tl, 198Au, 133I, 32P, and 90Sr-90Y. We used a model, such as slab-receptor exposed to beta-rays under conditions of broad parallel beam. The point of the maximum dose equivalent within the shell from 7mg/cm2 to 1, 000mg/cm2 in the slab-receptor was located at the depth of 7mg/cm2. We suggest to make use of dose equivalent at the depth of 7mg/cm2 as secondary limits to prevent non-stochastic effects on the skin and the lens, and to define it shallow dose equivalent.Moreover the conversion factors for the shallow dose equivalent to receptor-free air dose for beta-ray of energies (Emax) below 2.245MeV were examined. We proposed that the conversion fatter for the beta-rays is taken to be 1.1.