Assessment of doses from external exposure in contaminated areas resulting from the Fukushima Daiichi Nuclear Power Plant accident

Takahara, Shogo  ; Kimura, Masanori ; Kinase, Sakae   ; Ishikawa, Jun ; Suyama, Kenya; Hosoyamada, Ryuji; Homma, Toshimitsu

Dose assessment is one of the important issues to make decisions in contaminated areas resulting from the Fukushima Daiichi Nuclear Power Plant accident. The doses to inhabitants of contaminated areas should be assessed prospectively and retrospectively taking into account the impact from various exposure pathways. The external exposure from deposited radioactive materials of short-lived and long-lived is one of the most important pathways. In the present study, the radionuclide compositions have been evaluated by source term analysis taking into account 54 radionuclides. This analysis consists in evaluating the inventory and the fraction of the radionuclides that were released into the atmosphere. On the assumption that dose rate may be decreased due to the radioactive decay as well as weathering effects, we have assessed the dose for future and past at the contaminated areas. The assessed values are almost consistent with the measured ones during the first month.