Estimation of thoron progeny concentrations in dwellings with their deposition rate measurements

Based on the track-etching technique, a convenient, low-cost, time-integrating monitor was developed for measuring the deposition rate of attached thoron (220Rn) progeny indoors. Measurements of the deposition rates and concentrations of 220Rn progeny were simultaneously carried out in 13 dwellings throughout a year. Quite different deposition rates and concentrations of 220Rn progeny were found among those dwellings. However, seasonal variations of the deposition rates and concentrations were not significant in each dwelling. An average of (0.53±0.11) x 10-2 cm·s-1 was estimated for the deposition velocity of attached 220Rn progeny indoors, in fair agreement with most of the values for attached 222Rn progeny in dwellings in the literature. Significant correlation (r=0.981) was found between the deposition rates and concentrations of 220Rn progeny, and the deposition velocity for attached 220Rn progeny was relatively constant among the typical dwellings. It suggests that it is possible to estimate indoor 220Rn progeny concentrations using their deposition rates with the proposed simple measurement technique. (author)