Measurement of mixed samples of alpha and beta (gamma) nuclides using a high spatial resolution alpha-particle imager with Quantitative CMOS camera

Fujisawa, Makoto; Morishita, Yuki   ; Sagawa, Naoki; Kurosawa, Shunsuke*; Sasano, Makoto*; Hayashi, Masateru*

The measurement of alpha contamination, or alpha radiation, is important for the decommissioning of the Fukushima Daiichi Nuclear Power Station (FDNPS). It is very important to verify whether alpha particles can be visualized in a situation where alpha, beta, gamma-rays are mixed together. In this study, we applied our newly developed alpha imager to the measurement of actual samples containing a mixture of alpha, beta, and gamma nuclides, and verified its effectiveness. The alpha imager consisted of a qCMOS camera (ORCA-Quest (C15550-20UP)) and an optical microscope (BX53MRF-S from Olympus). A ZnS(Ag) scintillator with a thickness of 3.25 mg/cm was used for alpha measurements by placing the scintillator closely over a sample. An Am alpha standard source was measured to verify whether alpha particles could be measured. In addition, samples containing a mixture of alpha, beta, and gamma nuclides were measured. Image processing was used to extract clusters of alpha particles. By applying image processing, clusters of alpha particles were successfully extracted. When measuring a sample with a mixture of alpha, beta, and gamma nuclides, clusters of alpha particles could be confirmed. Although the sample had a higher beta activity than alpha activity, only alpha particles were successfully extracted. The developed alpha imager will be useful for contamination measurement in the site of FDNPS.