Exposure of the french population to environmental radiation from natural sources.
S. Billon, A. Morin, S. Caër, H. Baysson, J.P. Gambard, A. Rannou, D. Laurier and M. Tirmarche, IRPA 11, 24-28/05/2004, Madrid (Spain).
Natural radiation is the major source of exposure of the population in France. Previous work, based on results from measurement campaigns, has allowed to derive general estimates, but did not account for modifying factors (season, dwelling characteristics…) and was insufficient to reflect variability. When natural radiation exposure of the population has to be studied in parallel with health data (such as cancer incidence…), exposure data relative to population of interest should be corrected by the modifying factors. The aim of our work is to propose several corrections to derive more precise estimates of the true exposure of the French population.
National measurement campaigns were conducted in France since the 80’s by both the Institute for Radioprotection and Nuclear Safety (IRSN) and the Ministry of Health. Radon concentration measurements cover all the 96 French counties named “departments” (12261 indoor measurements). Dose rates due to gamma rays were measured in 59 departments (8737 measurements for indoor and 5294 for outdoor). Doses due to cosmic rays were calculated from city altitude with UNSCEAR (1993) formula.
Radon concentrations were corrected by a seasonal factor, accounted for dwelling type (house or building, old or recent) and weighted by department population density. The same corrections on dwelling type and population density were applied to gamma rays dose rates. Cosmic rays doses were weighted by population density.
Indoor radon concentrations had a crude average of 89 Bq m-3, ranging over all departments from 22 to 263 Bq m-3. The season and dwelling corrected average was 83 Bq m-3, varying from 19 to 297 Bq m-3. The national average was 63 Bq m-3, after corrections on season, dwelling and population density. The gamma dose rate averages were 55 and 46 nSv h-1 indoors and outdoors, respectively, ranging over all departments from 23 to 96 nSv h-1 indoors and from 25 to 85 nSv h-1 outdoors. Means were almost unchanged by corrections. After correction on population density, cosmic annual dose varied from 0.27 to 0.38 mSv, with an average of 0.28 mSv.
These corrections gave more precise estimates of the true exposure of the French population to natural radiation. Furthermore, exposure can also be estimated at different geographical levels (French administrative entities such as: regions, departments, job areas…), with a good representation of the exposure distribution, due to the important size of the data base. These estimates could be analysed in parallel with health indicators such as children leukaemia incidence, for example, in geographic studies.