A Simple Method for Estimating the Radioactive Contamination Level of a Standing Tree by Measuring its Surface Contamination Density

Abstract

This paper outlines the development of a simple method for estimating the radioactive contamination level of individual trees, for the purpose of contributing to forest management. This has become a difficult problem owing to the Fukushima Dai-ichi nuclear accident triggered by the earthquake of March 11, 2011 in Japan. To develop a simple estimating method, the relationship between the surface contamination density and the radiocesium concentration of the trees collected at Fukushima forests was investigated. The surface contamination densities were measured using a commercial GM-tube survey meter combined with a shielding box, which was filled with water to improve the detection limit by reducing background influence. The surveyed trees were felled and divided into bark, sapwood, and heartwood, and then the radiocesium concentrations were measured by gamma-ray spectrometry after grinding and oven-drying. The relation between surface contamination density and radiocesium concentration could be expressed by the function, y = Ax(B), in all of the trees surveyed. This finding suggests that it might be possible to estimate the degree of radioactive contamination of a standing tree by only measuring its surface contamination density using a simple GM-tube survey meter, and consequently, it will be helpful for future forest management.