Strontium-90 activity concentration in soil samples from the exclusion zone of the Fukushima daiichi nuclear power plant

Abstract

The radioactive fission product 90 Sr has a long biological half-life (18 y) in the human body. Due to its chemical similarity to calcium it accumulates in bones and irradiates the bone marrow, causing its high radio-toxicity. Assessing 90 Sr is therefore extremely important in case of a nuclear disaster. In this work 16 soil samples were collected from the exclusion zone (<30 km) of the earthquake-damaged Fukushima Daiichi nuclear power plant, to measure 90 Sr activity concentration using liquid scintillation counting. 137 Cs activity concentration was also measured with gamma-spectroscopy in order to investigate correlation with 90 Sr. The 90 Sr activity concentrations ranged from 3.0 ± 0.3 to 23.3 ± 1.5 Bq kg '1 while the 137 Cs from 0.7 ± 0.1 to 110.8 ± 0.3 kBq kg '1. The fact that radioactive contamination originated from the Fukushima nuclear accident was obvious due to the presence of 134 Cs. However, 90 Sr contamination was not confirmed in all samples although detectable amounts of 90 Sr can be expected in Japanese soils, as a background, stemming from global fallout due to the atmospheric nuclear weapon tests. Correlation analysis between 90 Sr and 137 Cs activity concentrations provides a potentially powerful tool to discriminate background 90 Sr level from its Fukushima contribution.