A novel method for simultaneous measurement of 222Rn and 220Rn progeny concentrations measured by an alpha spectrometer

The accumulation of Rn-222 and Rn-220 progeny in poorly ventilated environments poses the risk of natural radiation exposure to the public. A previous study indicated that satisfactory results in determining the Rn-222 and Rn-220 progeny concentrations by measuring the total alpha counts at five time intervals within 560 min should be expected only in the case of high progeny concentrations in air. To complete the measurement within a relatively short period and adapt it for simultaneous measurements at comparatively lower Rn-222 and Rn-220 progeny concentrations, a novel mathematical model was proposed based on the radioactive decay law. This model employs a nonlinear fitting method to distinguish nuclides with overlapping spectra by utilizing the alpha particle counts of non-overlapping spectra within consecutive measurement cycles to obtain the concentrations of Rn-222 and Rn-220 progeny in air. Several verification experiments were conducted using an alpha spectrometer. The experimental results demonstrate that the concentrations of Rn-222 and Rn-220 progeny calculated by the new method align more closely with the actual circumstances than those calculated by the total count method, and their relative uncertainties are all within +/- 16%. Furthermore, the measurement time was reduced to 90 min, representing an acceleration of 84%. The improved capability of the new method in distinguishing alpha particles with similar energies emitted from Po-218 and Bi-212, both approximately 6 MeV, contributed to realizing more accurate results. The proposed method has the potential advantage of measuring relatively low concentrations of Rn-222 and Rn-220 progeny in air more quickly via air filtration.