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

摘要

The radioactive fission product ⁹⁰Sr 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 ⁹⁰Sr 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 ⁹⁰Sr activity concentration using liquid scintillation counting. ¹³⁷Cs activity concentration was also measured with gamma-spectroscopy in order to investigate correlation with ⁹⁰Sr. The ⁹⁰Sr activity concentrations ranged from 3.0 ± 0.3 to 23.3 ± 1.5 Bq kg⁻¹ while the ¹³⁷Cs 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 ¹³⁴Cs. However, ⁹⁰Sr contamination was not confirmed in all samples although detectable amounts of ⁹⁰Sr can be expected in Japanese soils, as a background, stemming from global fallout due to the atmospheric nuclear weapon tests. Correlation analysis between ⁹⁰Sr and ¹³⁷Cs activity concentrations provides a potentially powerful tool to discriminate background ⁹⁰Sr level from its Fukushima contribution.