2019 年 54 巻 2 号 p. 103-114
This paper presents theoretical solutions for mean traveling distance of primary photons emitted from ground contaminated with radionuclide. Three typical patterns of radioactivity distribution are considered: (1) plane superficial source, (2) homogeneous volume source and (3) exponentially decreasing activity as a function of soil depth. Radiation dose rate can be easily estimated using the fluence rate of primary photons and the buildup factor. We assume the buildup factor is possible to be evaluated using the mean traveling distance. Comparisons between the results calculated in the present work and those obtained using detail Monte Carlo simulation codes indicate a good agreement for various radioactivity distributions and for photon energy ranging from 0.5 to 2 MeV. This methodology is very useful to estimate environmental radiation dose rates in a short time and can be practically used by residents and local government agents to evaluate impacts of radioactivity as well as utilizing it for studies of reducing the influence of radioactivity.
