MEASUREMENT OF THE INDOOR AND OUTDOOR ~(220)Rn (THORON) EQUILIBRIUM FACTOR: APPLICATION TO LUNG DOSE

摘要

A miniature four-chamber alpha track detector was developed that measures both ~(222)Rn (radon) and ~(222)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_(cq), 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_(cq) and the ~(220)Rn gas concentration. The lung dose from thoron in domestic or occupational surveys is often overlooked. The values of F_(cq) 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.