Some problems on measurement of activity size distributions with cascade impactors

Several types of low pressure cascade impactors have been used to measure the activity size distribution of 222Rn and 220Rn progeny. In spite of careful uses, reliability of the measured activity size distribution has not been established owing to a lack of the standard calibration method and facility. In these situations, the intercomparison experiments of the size distribution of 222Rn progeny using four low pressure cascade impactors were conducted in the reactor room of the KUCA of Kyoto University. From the comparison results, it is suggested that of the discrepancy between impactors originate mainly the difference of the jet to collecting plate distances of the impactors. (author)