Abstract
The Fukushima nuclear power plant disaster which occurred by the East Japan great earthquake caused the extensive radioactive contamination. It is very difficult to know how long this radioactive contamination continues. However, when taking into consideration the future decontamination work, the refuge duration, etc., it is considered one of the important factors. I tried a speculation of the ecological half-life of 137Cs in the animal which inhabits the Fukushima nuclear power plant disaster contaminated zone based on the several data. The following data were referred to for a speculation of ecological half-life. 1) The half-life of the 137Cs whole body count originating radioactive fallout to Japan by nuclear test in the atmosphere (1964-1969) and the Chernobyl nuclear plant accident of 1986 (Uchiyama,M. et al. 1996), 2) The ecological half-life of the 137Cs in fish of lake in Norway (Jonsson,B. et al. 1999) and UK (Smith,JT. et al. 2000) , and 3) The 137Cs pace of decrease in the Chernobyl contaminated zone animal body in 1997 to 2005 (our report of previous JRR meeting: Nakajima,H. et al. 2006). It was speculated that the ecological half-life of 137Cs of the beginning in Fukushima is about 1.5 years.
