Imaging techniques for radiocesium in soil and plants

Abstract

Various radioisotope imaging techniques have been used at the Graduate School of Agricultural and Life Sciences, University of Tokyo, to analyze samples containing radiocesium (137 Cs and 134 Cs). There are two types of samples: (1) environmental samples contaminated by the fallout from the Fukushima Daiichi nuclear power plant accident, which contain relatively low concentrations of radiocesium and (2) laboratory samples from tracer experiments conducted at the radioisotope institution containing relatively high concentrations of 137 Cs. The first technique used to visualize radiocesium in soil and plants was radioluminography (RLG). RLG, which makes use of an imaging plate, has a dynamic range that is large enough to detect both environmental and tracer-added samples. To quantify radiocesium distributions, the samples were frozen and sliced before contact with the imaging plate. This freezing procedure after sampling is for preventing radiocesium movement during slicing and measurement of 137 Cs distribution. After slicing, two detection methods were employed: RLG and microautoradiography (MAR). MAR is the conventional and older method for imaging radioisotopes based on the daguerreotype process. We applied this method to frozen sections and obtained 137 Cs distributions at a higher resolution than with RLG. Following this, we employed a non-destructive method for imaging 137 Cs movement in a living plant. We developed the visualization technique called real-time radioisotope imaging system and then demonstrated 137 Cs movement from soil to rice plants using a chamber containing paddy soil, water, and rice plants. Lastly, 42 K obtained by 42Ar-42 K generation enabled a comparison between the movement of 137 Cs and 42 K. The mechanism of Cs transport has been reported to have some relationship with the K transport system, so experiments using both 137 Cs and 42 K would be useful for clarifying the mechanism in more detail.