Background correction of personal dose distributions by a novel unfolding algorithm

The dosimetry service Seibersdorf monitors more than 20,000 persons with typical monitoring period of one month. The use of thermoluminescence (TL)-dosemeters during the last 30 years allows measurements of even low dose values (some 10 μSv) with sufficient uncertainty. Consideration of the natural background contribution or transport dose which needs to be subtracted from the measured dose requires special protocols which differ significantly from country to country. The chosen protocol has not only a strong influence on the individual dose values (especially for low doses) but changes significantly the whole dose distribution function, as well as the corresponding statistical describing parameters (mean doses, median values, etc.) of these distributions. On the basis of the measured (uncorrected) distribution function the attempt was made to extract both the background doses as well as the remaining occupationally caused dose contribution. For this approach the uncorrected dose values of all customers from several years were analysed and a superposition of two independent log-normal distributions was assumed. By means of a new unfolding algorithm both components were isolated and the corresponding parameters were calculated. The paper gives a detailed description of the procedure and summarises the resulting dose distributions. (authors)