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

Morishita, Yuki; Kurosawa, Shunsuke*; Yamaji, Akihiro*; Hayashi, Masateru*; Sasano, Makoto*; Makita, Taisuke*; Azuma, Tetsushi*

Scientific Reports (Internet), 11(1), p.5948_1 - 5948_11, 2021/03

AA2020-0761.pdf:1.59MB

https://doi.org/10.1038/s41598-021-84515-z

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 umFWHM with a zoom range of 5 x. Also, the spatial resolution for the plutonium dioxide particle was 302.7 umFWHM 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.

Plutonium particle imaging using an ultra-high-resolution alpha imager

Morishita, Yuki; Kurosawa, Shunsuke*; Yamaji, Akihiro*; Hayashi, Masateru*; Sasano, Makoto*; Makita, Taisuke*; Azuma, Tetsushi*

no journal, , 

It is crucial in considering internal exposure when workers inside nuclear facilities inhale plutonium particles. The internal exposure dose is strongly affected by the particle size distribution defined as activity median aerodynamic diameter (AMAD). To acquire the AMAD value at the working site of the nuclear facility, we developed an alpha imaging detector using an optical camera and an optical microscope. Then, we applied it for plutonium particle measurements. The ZnS(Ag) scintillator sheet and a plutonium particle were close to each other. Alpha particles were absorbed in the ZnS(Ag) scintillator and were converted to scintillation light. An Electron Multiplying (EM) CCD camera was mounted on top of the optical microscope to capture scintillation light. The zoom range was adjustable from 5x - 20x. When using the zoom range of 20 x, the resolution and Field of View were 0.81 um/pixel and 412.9 um 412.9 um, respectively. The Full width at half maximum (FWHM) of an alpha particle was evaluated to be 17.9 um. Locations of individual alpha particles from a plutonium particle can be identified in real-time. The number of alpha counts was agreed with those measured using a commercial ZnS(Ag) scintillation counter. The measured alpha counts will be able to convert to radioactivities and AMAD. Thus, the ultra-high-resolution alpha imager will be promising plutonium particle measurements at the working sites of nuclear facilities.