A personal 222Rn and gamma-ray detector has been developed. The detector precision is limited only by the Poisson counting error and has a lower limit of detection in this study of 4.5 kBq m-3 h (4 pCi L-1 day). The detector was used in a study of 52 homes in Illinois to measure the personal exposure vs. the simultaneous exposure on all levels of the home. The ratio of personal exposure to basement 222Rn concentration averaged 0.22, with a high degree of scatter (R2 = 31%). The ratio of personal exposure to first floor 222Rn concentration was 0.71, with good correlation (R2 = 85%). In the absence of personal monitoring data, the best estimate of personal exposure appears to be from measurements in the first-floor living space of the home.

To provide detailed information for bronchial dose estimates, aerosol particle size distributions, and radon gas concentration, measurements were made in six residential homes and three laboratory rooms in different office buildings in the city of Ottawa. In the literature, most particle size distribution measurements are taken with samplers operating for a few days at most. In this study, the particle size samplers collected the samples from 77 to 162 d. The equilibrium factor determined from the long-term measurements ranged from 0.6 to almost 1 with an average of 0.75. Even though radon concentrations were quite different between residential setting and office buildings, the average equilibrium factor was similar in the two different indoor environments. The results suggest that at least in some basements, if they were occupied, the radon dose would be about twice as high as normally estimated from the conventional F(eq) value of 0.4.

A miniature four-chamber alpha track detector was developed that measures both (222)Rn (radon) and (220)Rn (thoron), in duplicate. Using this detector and the previous long-term measurements of the (220)Rn decay products (212)Pb, and (212)Bi, an equilibrium factor, F(eq), is derived for both outdoor and indoor (220)Rn environments (0.004±0.001 outdoors and 0.04±0.01 indoors). The lung airway dose can then be calculated from a dose factor from UNSCEAR that requires the equilibrium equivalent thoron concentration (EEC), i.e. the product of F(eq) and the (220)Rn gas concentration. The lung dose from thoron in domestic or occupational surveys is often overlooked. The values of F(eq) for thoron in several published studies are in general agreement with the values reported here. Thus, a long-term alpha track measurement of thoron multiplied by an appropriate indoor or outdoor equilibrium factor yields the EEC, which can be used to assess bronchial lung dose.

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