SEM-EDX Observation of Diatomaceous Earth at Radioactive Paddy Soils in Fukushima, Japan

Diatomaceous earth collected from Noto Peninsula, Ishikawa Prefecture, was observed by scanning electron microscopy (SEM) equipped with energy dispersive x-ray analyzer (EDX). These samples had suffered radiation exposure in a radioactive paddy field in Baba, Fukushima Pref., Japan, after the Great East Japan Earthquake, on March 11, 2011. Energy-dispersive x-ray fluorescence (ED-XRF) analysis and Ge semiconductor detector found not only major elements but also radionuclides, such as¹³⁴Ce, ¹³⁷Cs, ⁸⁹Sr, and⁹⁰Sr, in the paddy field in Baba. After 1 year, SEM-EDX quantitative analyses of diatoms and clay minerals (mainly montmorillonite) clearly indicated concentration of radionuclide, such as I, Cs, Ba, Nd, Th, U, Np, and Pu, suggesting absorption of both radionuclide and stable isotope elements from radioactive polluted paddy soils. The leak of radioactivity of ¹³⁷Cs, part of ⁹⁰Sr, and the traces of some radionuclide are originated from Fukushima Daiichi Nuclear Power Plant (FDNPP) accident. The diatom–clays–radionuclide interaction in the polluted paddy soils in Fukushima could be effective as the shield for low-level radioactive waste at the geological disposal.