Abiko International Open-Air Art Exhibition has been held since 1998 on the fields and forested hills near Fusa rail way station of JR Narita line. The Exhibition is worldly well known and highly appreciated among artists and art lovers.

On the 15th Exhibition in 2012 we learned that the members of the organizing committee, residents of Fusa, participating artists from various parts of the world, and viewers were worried about fallout of radioactive materials spewed from the Fukushima Daiichi Nuclear Power Plants. Then we volunteered to measure radiation levels on the fields and hills where works of art were exhibited. Since then we have kept coming back when the Exhibition is held.

The set of three data of 2012, 2014 and 2016 tells that decrease of the radiation levels in these four years is faster than that predicted from the half-life of 134Cs and that of 137Cs. This fact may be accounted for by continuous efforts of the residents and the office of local government to decontaminate, and by “weathering”, that is washing away radioactive contaminants by frequent rains.