Estimation of shallow dose equivalent for beta-rays by Monte Carlo method

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 7 mg/cm2 to 1,000 mg/cm2 in the slab-receptor was located at the depth of 7 mg/cm2. We suggest to make use of dose equivalent at the depth of 7 mg/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 (Esub(max)) below 2.245 MeV were examined. We proposed that the conversion facter for the beta-rays is taken to be 1.1. (author)