Temporal variation of monthly ¹³⁷Cs deposition observed in Japan: effects of the Fukushima Daiichi nuclear power plant accident.

Monthly (137)Cs depositions from March 2011 to April 2012 were reported at monitoring stations within about 250 km from the Fukushima Daiichi NPP. The monthly (137)Cs deposition at each station decreased with apparent half-lives of 11-14 d during the period from March to June 2011, and after July 2011 its decrease rates changed. Second peaks of the monthly (137)Cs deposition occurred in February-April 2012, which may be supported by resuspension of (137)Cs bearing particles.