Plutonium dioxide particle imaging using a high-resolution alpha imager for radiation protection

Abstract

The internal exposure of workers who inhale plutonium dioxide particles in nuclear facilities is a crucial matter for human protection from radiation. To determine the activity median aerodynamic diameter values at the working sites of nuclear facilities in real time, we developed a high-resolution alpha imager using a ZnS(Ag) scintillator sheet, an optical microscope, and an electron-multiplying charge-coupled device camera. Then, we designed and applied a setup to measure a plutonium dioxide particle and identify the locations of the individual alpha particles in real time. Employing a Gaussian fitting, we evaluated the average spatial resolution of the multiple alpha particles was evaluated to be 16.2 ± 2.2 μmFWHM with a zoom range of 5 ×. Also, the spatial resolution for the plutonium dioxide particle was 302.7 ± 4.6 µmFWHM due to the distance between the plutonium dioxide particle and the ZnS(Ag) scintillator. The influence of beta particles was negligible, and alpha particles were discernible in the alpha–beta particle contamination. The equivalent volume diameter of the plutonium dioxide particle was calculated from the measured count rate. These results indicate that the developed alpha imager is effective in the plutonium dioxide particle measurements at the working sites of nuclear facilities for internal exposure dose evaluation.

Alpha-ray imaging with alkali copper halide scintillator

“…Thus, we have developed an alpha-ray imaging detector with a high position resolution consisting of a scintillation sheet, optical microscope and Complementary Metal Oxide Semiconductor (CMOS) camera. Our group reported that the similar detector to our detector using a thin sheet of Ag:ZnS scintillator, and a position resolution was estimated to be 16 μm for alpha rays [1]. However, further improvement for the position resolution is required, and final goal is 0.1-1 μm.…”

“…Radiation monitoring is an important technique for the safety decommissioning of the Fukushima Daiichi Nuclear Power Plant (FDNPP), and the internal exposure for workers is a crucial matter for human protection from radiation in FDNPP [1]. Especially, alpha-emitting dusts such as plutonium dioxide particles must be controlled to avoid internal exposure, and detailed information on the radiation dose distribution and alpha-emitting dust inside FDNPP is necessary to decommission.…”