Determination of time-average equilibrium factor between radon and its progeny using SSNTDs

To evaluate the equilibrium factor between radon and its progeny in air, the measurement system made up of opened solid state nuclear track detector and filtered one is established. The HURC(Hanyang University Radon Cup) is used as a detector chamber in combination with a CR-39 track detector. The methodology using track density ratio of two SSNTDs, suggested by Domanski, is used to determine the equilibrium factor. To test the validity of this relationship between the equilibrium factor and track density ratio, calibration experiments are carried out with the pair-cup system for radon and its progeny in the radon chamber at the National Radiological Protection Board(NRPB, UK). To test the performance of the pair-cup system, intercomparison experiments are carried out with another radon and its progeny detectors in radon chamber at the Korea Research Institute of Standards and Science(KRISS, Korea). The calibration factor associated with the filtered SSNTD for radon, obtained from calibration experiments, is 9.59±0.49 Bq·m-3 per tracks·cm-2·d-1 and the other is 1.6x10-3±1.6x10-4 WL per tracks·cm-2·d-1 for radon progeny. The results of the validity-test found that the methodology using the track density ratio between the open and filtered cup are applicable to determination of the equilibrium factor for a long-term exposure period, from 100 kBq·h·m-3 to 200 kBq·h·m-3 of accumulated radon concentration. Besides, the pair-cup system reflects well the change of equilibrium. The methodology and the established system can apply to measurement of the time-average equilibrium factor in underground mines or basements associated with high radon exposures