intercalibration-intercomparision exercise. Reportedly the University of Hong Kong has some experience on this subject.
With regard to radon electret detectors occasional deviations from the otherwise almost neglegible drop in surface potential (± 1 volt/month) of unexposed radon electret detectors have been noted. This effect needs to be verified and the cause identified, e.g. by conducting measurements only at the beginning and end of a 3 months-period, equivalent to the longest exposure period used in the field at this time. Repeated measurements during this test period should be avoided to reduce the probability of mishandling the electrets. Unexposed electrets being tested need to be stored under identical and constant exposure conditions with regard to dust, humidity, temperature and environmental gamma dose rate levels.
6.2. IDENTIFICATION OF RELATIVE SOURCE TERM CONTRIBUTIONS
TO INDOORS RADON LEVELS
Presently available results indicate a strong influence of the building material used in Hong Kong as the main source for the elevated radon levels. However, it is unknown to what extent radon from the subsoil may also
contribute to the indoor radon levels. Such a contribution can be in the form of radon diffusion through the foundation or transport through cracks and openings into the lower parts of the building. Another possible source term could be active radon transport from the subsoil into the frequently built multi-storey high-rising buildings due the "chimney effect", i.e. thermal gradients causing radon to be sucked from the lower parts of the building and transported through its ducts, ventilation pipes, etc. to the upper floors. Before considering regulating the material industry it is essential to establish which relative contribution to the radon levels indoors results from radon from the subsoil vs. radon from the surrounding walls.
6.3. UNATTACHED FRACTION AND EQUILIBRIUM FACTOR
Based on the survey data the ultimate goal will be dose- and risk assessment calculations for the Hong Kong population. In the exposure-dose conversion the fraction of unattached radon decay products (fp) plays a significant role. Depending on the lung model used, the mean bronchial dose (normalized per WLM) varies from about 10 mGy to 180 mGy over the typical
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