Influence of 220Rn on 222Rn measurement in Chinese cave dwellings

Alpha track detectors (ATDs) are widely used for measurement of indoor Rn-222 concentration. However, some results showed there were quite differences of Rn-222 concentration in some Chinese cave dwellings by using different kinds of ATDs. The abnormal results had caused a special attention. Further experiments found some filter membranes used with some detectors had very large air exchange rates, that means Rn-220 gas can also get into diffusion chamber through filter with Rn-222 gas together. In this way, Rn-222 concentration would be overestimated for the disturbance of Rn-220. Since the Rn-220 concentrations are very high (152 similar to 296Bq m(-3)) in some cave dwellings north west in China, its contribution should not be neglected.