In nuclear facilities, it is necessary to know the size of alpha particles emitted in the workplace in order to evaluate the internal exposure of workers. Until now, imaging plates have been used, but these detectors were not capable of real-time measurement. In addition, imaging plates are sensitive to radiation other than alpha rays, so it was necessary to distinguish between alpha rays and other types of radiation.
Yuki Morishita (researcher at Japan Atomic Energy Agency) collaborated with Associate Professor Shunsuke Kurosawa, Assistant Professor Akihiro Yamaji (affiliated with the IMR), Masateru Hayashi, Senior Researcher Tetsushi Higashi, Researcher Osamu Sasano, and Researcher Taisuke Makita (Mitsubishi Electric Corporation) to develop the world’s first ultra-high resolution alpha ray imaging detector for nuclear power applications.
This device combines an extremely thin scintillator, an electron-multiplying CCD camera, and an optical microscope to detect only alpha rays. When applied to a plutonium (Pu) sample, we succeeded in visualizing each alpha ray in real time. In addition, we confirmed that the position resolution of alpha rays was 16 μm, which exceeds the performance of conventional imaging plates (25 μm).
Since this device can visualize the position of each alpha ray, we have devised a method to directly evaluate the counting rate of individual plutonium particles from the number of alpha rays and determine the particle size (equivalent particle diameter). We believe that this will enable the evaluation of the particle size distribution of plutonium particles in real time at the work site.
Going forward, we plan to improve the accuracy of this device by applying it to various samples. Furthermore, we hope to contribute to the evaluation of internal exposure doses at work sites and radiation safety by applying it to the measurement of actual samples from the Fukushima Daiichi Nuclear Power Station of Tokyo Electric Power Company Holdings, Inc.
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