The radon survey plan developed is based on the available NRE-data as derived from the progress report of this IAEA-project by Dr. C. K. MAN together with data from various studies published by the above research teams (P, C, U, EPD, R).
All publications made available are listed in the "List publications on the natural radiation environment from Hong Kong" in the Appendix 1. Most of them are in the form of internal technical reports and not easily available in the open literature.
5.1. SOURCE TERM AND MODIFYING FACTORS
The geology of the substrate of the Hong Kong area shows two distinct groups of materials:
a) igneous rocks (granites, pegmatite) for the districts of Kowloon, Tuen Mun, the southern part of the New Territories and the Central and Eastern part of Hong Kong Island;
b) acidic volcanic rocks, sedimentary rocks and reclamation for all other
areas.
All areas with the highest population density are in the granitic region. A survey of soil samples from different locations showed that the mean uranium-, radium-, thorium- and potassium activity concentration value are 93, 77, 146 and 817 Bq/kg. These U- and Th-values are 350 %, respectively 600 % higher then global averages (UNSCEAR-values). In some locations, e.g. Tuen Mun, levels exceed the corresponding values found in the Chinese high background radiation area of Guangdong, for example in the case of potassium by about 100%.
Sofar it was not possible to correlate the different radionuclide concentration values in the subsoil of the various regions with corresponding indoor radon levels. It has to be emphasized though that a relatively small number of sites (60 locations) was investigated, limiting the statistical significance of these findings.
The type of ventilation was found to be of major influence on radiation levels in Hong Kong. Rooms equipped with the frequently used window-type air conditioners have a mean radon activity concentration over 400 % higher than rooms with natural draught ventilation only (level of statistical significance a = 0.05). This is due to the fact that during summer months most such units are
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