e) grab sample measurements of radon with a short time constant ("radon sniffing") to identify radon entry routes, such as openings, gaps, cracks,
etc.
f) simultaneous grab sample measurements of working level to determine the age of air and the equilibrium factor;
g) radon- and thoron exhalation measurements from walls and floors;
h) gamma spectrometry of samples from walls, floors, subsoil, and analysis for 238U, 232Th, 226Ra and 4oK;
i) ventilation conditions in these test buildings and determination of the influence of air conditioning on the radon/thorium and decay
product activity concentration.
The sample size for each of the above sub-programmes should be such that the statistical significance of potential differences between averages from different data sets can be tested, e.g. by the two sided t-test at a level of significance of a = 0.05 or better.
8. CONCLUSIONS
All available information on the natural radiation environment (NRE) of the Hong Kong area was reviewed in order to use the pooled information for identifying additional topics to be adressed and to design an optimal survey plan. From the several pilot-type surveys conducted by the Hong Kong Polytechnic and other local research institutions the NRE of Hong Kong can be characterized as an area of partly significantly elevated background radiation. Activity concentration values for some natural radionuclides in the subsoil, building materials and indoor air are generally above global average values as published by UNSCEAR and are frequently comparable to the corresponding values found in the high background radiation areas of Guangdong (China, P.R.). However, at present the available data cannot be used for the assessment of statistically significant dose distributions, since they are largely derived from pilot studies associated with large uncertainties.
Several scientific issues have been identified in need of clarification of the situation in Hong Kong, such as: quantification of the different components
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