Radioactivity in building materials-effects on indoor radon concentrations and gamma doses

Full text: Many building materials contain levels of radioactivity which are considerably higher than the natural levels in soil. This has the potential to cause elevated radon (222Rn) levels in indoor air and to increase the contributions to the total annual effective dose to occupants of buildings from gamma and beta radiation. This paper presents a brief summary of measurements of the radium (226Ra) concentration in soil, phospho-gypsum plaster-board, granite and zircon, and of the 222Rn exhalation rates from these materials. Estimates of the incremental increase in the radon concentration in indoor air resulting from the use of these materials are compared with the action levels of 200 Bq m-3 set by the National Health and Medical Research Council and the results of an Australia-wide survey of radon levels and annual gamma doses in homes (Langroo, M.K., et al., Health Phys. 61:753-761; 1991). A simple model of indoor radon concentration shows that the crucial factor in determining the effect of exhalation of radon from building materials on the indoor radon concentration is ventilation. The incremental gamma dose resulting from the use of these materials is also estimated, using typical occupancy factors, and compared with the results of the Langroo survey