Distribution of strontium-90 in soils affected by Fukushima dai-ichi nuclear power station accident in the context of cesium-137 contamination

Sr-90 and Cs-137 activity concentrations were determined by radiometric methods in 76 soil samples (soil, litter, rain gutter deposit, and roadside sediment samples) affected by the Fukushima Dai-ichi Nuclear Power Station (FDNPS) accident and collected from the Fukushima exclusion zone. The Sr-90 and Cs-137 activity concentrations were in the range of 3 to 1050 Bq kg(-1) (median 82 Bq center dot kg(-1)) and 0.7 to 6770 kBq center dot kg(-1) (median 890 kBq center dot kg(-1)), respectively (decay correction date: March 15, 2011). A strong positive correlation was found between Sr-90 and Cs-137 activity concentration and higher mobility of Sr-90 was confirmed in Japanese soil samples. The activity ratio of Sr-90/Cs-137 in 85% of all samples was in the range of 5.0 x 10(-5) to 5.0 x 10(-4) with a median of 1.2 x 10(-4). From the activity ratio values it was concluded that the Sr-90 released to the atmosphere was only around 0.0003 0.02 PBq which is negligible compared to the Chernobyl accident (similar to 10 PBq) or other nuclear accident contaminations. From the standpoints of radioecology and radiation safety, Cs-137 remains the primary pollutant of the FDNPS accident.