Methodology for Evaluating Surface Collection Efficiency of Filters Used for Ambient Radioactive Aerosols

抄録

Air filters are widely used to collect ambient radioactive aerosols at nuclear facilities. In the measurement of alpha-emitting radionuclides, the surface collection ef ficiency (SCE) is crucial for filter selection because their collection inside the filter matrix causes the energy spectrum degradation. However, SCEs reported in previous studies varied depending on methods, even for the same filters. In this study, the SCEs evaluated by the conventional methods were examined using Monte Carlo simulations. Radon progeny in a radon exposure chamber was collected on filters, and the SCEs for the filter were calculated by applying the conventional methods to its alpha energy spectrum measured using a silicon semiconductor detector under vacuum conditions. The SCEs were also evaluated by adjusting the alpha energy spectrum simulated using a particle and heavy ion transport code system (PHITS ver. 3.02) to the measured spectrum. As a result, one of the three conventional methods provided the best estimate of SCEs for filters, which agreed well with the simulated SCEs. This method shows the lowest SCEs compared to those evaluated by the conventional methods, indicating that the SCEs reported in previous studies may have been overestimated.