An exploratory study on 222Rn measurement method using a length-compensated proportional counter

A length-compensated proportional counter (LCPC) is widely employed as the primary standard for the activity concentration of beta-emitting radioactive noble gases. In this study, an absolute measurement method using LCPC for 222 Rn and its progenies, including a Monte Carlo-based threshold correction method, was investigated. Three proportional counters with different lengths (LL, M, and SS) were employed in the LCPC system. 222 Rn was injected into the LCPC and alpha spectra were acquired. Three alpha peaks were observed: 5.5 MeV from 222 Rn, 6.0 MeV from 218 Po, and 7.7 MeV from 214 Po. The anode operating voltages were determined from the threshold-corrected plateau curves. The measured 222 Rn activity concentrations were compared with those obtained using a calibrated inner-through type ionization chamber (IC). Although the IC calibration factor was provisional, the LCPC results were in good agreement with the IC measurements, within 5 %. This agreement may indicate that the measurement method investigated in this study could be practically applicable to absolute 222 Rn measurements.