The self-absorption correction factors for Pb concentration in mining waste and influence on environmental radiation risk assessment.

The radioactive lead isotope Pb occurs in waste originating from metal smelting and refining industry, gas and oil extraction and sometimes from underground coal mines, which are deposited in natural environment very often. Radiation risk assessment requires accurate knowledge about the concentration of Pb in such materials. Laboratory measurements seem to be the only reliable method applicable in environmental Pb monitoring. One of the methods is gamma-ray spectrometry, which is a very fast and cost-effective method to determine Pb concentration. On the other hand, the self-attenuation of gamma ray from Pb (46.5 keV) in a sample is significant as it does not depend only on sample density but also on sample chemical composition (sample matrix). This phenomenon is responsible for the under-estimation of the Pb activity concentration level often when gamma spectrometry is applied with no regard to relevant corrections. Finally, the corresponding radiation risk can be also improperly evaluated. Sixty samples of coal mining solid tailings (sediments created from underground mining water) were analysed. Slightly modified and adapted to the existing laboratory condition, a transmission method has been applied for the accurate measurement of Pb concentration . The observed concentrations of Pb range between 42.2 ÷ 11,700 Bq·kg of dry mass. Experimentally obtained correction factors related to a sample density and elemental composition range between 1.11 and 6.97. Neglecting this factor can cause a significant error or underestimations in radiological risk assessment. The obtained results have been used for environmental radiation risk assessment performed by use of the ERICA tool assuming exposure conditions typical for the final destination of such kind of waste.