Innovation of a continuous radon equilibrium factor monitor by a novel twin air-flow ion pulse ionization chamber system

A novel monitor based on two airflow ion pulse ionization chamber (IPIC) counters was designed, simulated, constructed, and validated for rapid measurement of the radon equilibrium factor. The monitor consists of two identical IPIC detectors. One includes a filter, which effectively blocks the entry of radon progeny (IPIC/filtered); thus, its response is generally proportional to the activity concentration of radon gas alone. The second detector lacks this filter (IPIC/unfiltered), so its response reflects the combined activity of both radon and progeny in the surrounding air. The response of the detectors to alpha particles from radon and progeny was calculated using Geant4 Monte Carlo code. A comprehensive mathematical model was developed to determine the radon equilibrium factor. Field measurements were conducted in both laboratory and residential environments, and results were compared with those from passive detectors. The findings showed that measured equilibrium factors fell within the expected range. Moreover, the proposed monitor demonstrated faster response and higher accuracy than conventional methods, enabling continuous real-time monitoring of the equilibrium factor in both residential and occupational settings. The monitor has strong potential to enhance the assessment of internal radiation dose due to radon exposure and improve continuous radon monitoring.