ニッケル63を用いたエアロゾル中和器の電荷調整性能評価

抄録

In Japan, Americium-241 (Am-241) has long been used as an ion source for aerosol neutralizers in Scanning Mobility Particle Sizers (SMPS). However, due to the manufacturer’s discontinuation of production, sales by the Japan Radioisotope Association ceased at the end of 2021. To address this issue, we developed a prototype aerosol neutralizer using a sealed Nickel-63 (Ni-63) source with an activity of 100 MBq as an alternative ion source. According to Japanese regulations, the lower limit for a sealed Ni-63 source is 100 MBq. Since the activity of the source used in our prototype does not exceed this threshold, the device is not subject to regulation, and no notification to the Nuclear Regulation Authority is required for its use, modification, or disposal. In this study, we evaluated the charge conditioning performance of the Ni-63 aerosol neutralizer by comparing it with the conventional Am-241 neutralizer and the charging probability values used in SMPS. The results showed that, under certain conditions, the differences were non-negligible compared to the reference values. However, in most cases, the particle concentration and charging probabilities were within acceptable ranges. These findings confirm that Ni-63 is a viable alternative ion source, particularly given the unavailability of Am-241 in Japan.