Measurements of background radiation doses for small-sized mammals in forests - Mouse (Apodemus argenteus) and shrew mole (Urotrichus talpoides)

Mouse (Apodemus argenteus) and shrew mole (Urotrichus talpoides) were selected as representative small-sized animals of a forest ecosystem in this study, and their radiation doses derived from natural radiation source, i.e. environmental γ-rays, Rn and internal radionuclides, have been measured in a beech and oak forest in Rokkasho, Aomori, Japan during FYs 2006-2007. Mean environmental γ-ray dose rates were 30 nGy h^-1 at 5 cm height above ground in those forests, and 28 nGy h^-1 in simulated burrows at 5 cm depth drilled in the campus of our institute. Mean atmospheric ²²²Rn concentrations in those forests and in the burrows were 6.0 Bq m^-3 and 0.29 kBq m^-3 and 0.29 kBq m^-3, respectively. Dose rates delivered to the lung and the bronchus by ²²²Rn and its progenies were calculated to be 0.25 μGy h^-1 and 0.33 μGy h^-1 for the mouse, and 0.41 μGy h^-1 and 0.55 μGy h^-1 for the shrew mole, respectively. The mean internal dose rates in the mouse and the shrew mole were estimated as 0.048 μGy h^-1 and 0.41 μGy h^-1, respectively, with dose conversion factors using a very simple phantom. The difference between them was mainly attributed to body burden of ²¹⁰Po, which was 9 times higher in the shrew mole than in the mouse. (author)