Age-Dependent Dose to Red Bone Marrow from Natural Radon, Thoron and 40K

Abstract

The age-dependent radiation dose to the haematopoietic tissue of bone marrow has been calculated for exposure to radon, thoron and their daughter products, for the foetus, children and adults. The component of dose due to pure radon is dependent on the fat content of the marrow, since the solubility of radon in fat is about sixteen times that in tissue. The mean dose equivalent µSv to the total active marrow is estimated for a range of fat cell diameters from 25 to 200 µm, taking account of the percentage cellularity and distribution of active marrow as a function of age. Similarly the dose due to the inhalation of short-lived radon daughters was estimated, based on measurements in blood and marrow, modified to allow for the greater deposition of daughter products expected in children. An estimate of the age-dependent dose from long-lived radon daughters was made from uranium miners and natural exposure data. Dose estimates were made for the average UK indoor exposure to radon gas of 20 Bq.m-3 and an equilibrium equivalent thoron concentration of 0.3 Bq.m-3. The annual radon and thoron derived dose to the active marrow of the newborn was calculated as 30 and 40 µSv respectively. For a 10 year old child, the radon and thoron derived annual doses are 70 and 40 µSv and for the 40 year old adult 90 and 30 µSv, respectively.