Determination of long-lived radionuclides and stable elements by ICP-MS, and its application to the study of environmental radioactivity

Isotopes of U and Pu in environmental samples were successfully determined by inductively coupled plasma mass spectrometry (ICP-MS). Stable elements related to radiocesium were also analyzed for samples collected in the forests by ICP-MS. The 235U/238U atom ratios in soil and plant samples collected on the JCO grounds after the criticality accident were notably higher than the natural ratio, 0.00725, suggesting the possible contamination of U. The isotopic composition of enriched U released from the facilities was estimated from the positive correlation between U concentration and 235U/238U atom ratio in soil samples. The 240Pu/239Pu atom ratios in environmental materials were varied widely depending on the sources of Pu. Compared with alpha spectrometry, the ICP-MS method has significant advantages in terms of its simple analytical procedures, prompt measurement time and capability of determining the 240Pu/239Pu atom ratio. A good correlation between radiocesium and stable Cs in mushrooms and plants was observed for each sampling site independently. The ratio between radiocesium and stable Cs might be useful for judging the equilibrium of deposited radiocesium in different parts of a forest ecosystem. The stable Cs analyses might be also useful to predict the long-term radiocesium contamination of mushrooms and plants. (author)