ミッシュメタル含有放射性核種からの線量評価

抄録

Radionuclides contained in three kinds of misch metal products and two kinds of ingots were analyzed using a Ge (Li) semiconductor detector. Lanthanum-138 (¹³⁸La) and several daughter nuclides derived from thorium and uranium series were detected in all samples.All misch metal products and ingots were determined to be radioactive consumer products (RCP), although they have not been regarded as RCP in Japan. ¹³⁸La showed the highest nuclide content rate of all the radionuclides, and the lanthanum metal ingots displayed the highest specific activity at 720m Bq·g^-1. The maximum external effective dose was estimated to be 3.7m Sv when a metal match was carried for 8, 760 hours at 1mm from the skin. The calculated effective dose under some conditions exceeded 10μ, Sv per year.This value corresponded to the exemption standard proposed by the UK's National Radiological Protection Board.Individuals working with large amounts of RCP should be appropriately protected.