Indoor 222Rn measurements using an activated charcoal detector

A commercially available activated charcoal detector for measuring 222Rn activity concentrations in air was calibrated with known amounts of 222Rn and examined in terms of air luminescence counts and interferences from 220Rn and 219Rn. The results for conditions normally encountered indoor indicate that the detector is simple and reliable. The method has been applied to assay indoor 222Rn activity concentrations in 387 homes in Tokyo and the adjacent four prefectures, which ranged from 0.7 to 140 Bq/m3 and averaged 22.7 Bq/m3.