Radiological characteristics and investigation of the radioactive equilibrium in the ashes produced in lignite-fired power plants

High concentrations of natural radionuclides in building materials can result in high dose rates indoors, from both internal and external exposure. In dose calculations, the main radionuclides of interest are 226Ra, 232Th and 40K. Usually much attention is paid to 226Ra due to Rn-222 exhalation and the subsequent internal exposure. Other radionuclides of the uranium series such as 238U and 210Pb, emitting low energy photons are not usually determined and an assumption of radioactive equilibrium is made. The above assumption is seldom checked mainly because of the difficulties in the γ-spectroscopic analysis of low energy photons. For the determination of radionuclides emitting low-energy photons, in samples like building materials where intense self-absorption of the photons exists, a method for self-absorption correction has been developed. The method needs as input the linear attenuation coefficient μ for the material under analysis. This paper presents:

1. Correlations in the form μ=f(ρ,E) developed for the estimation of the linear attenuation coefficient μ (cm-1), as a function of the material packing density (g cm-3) and the photon energy E (keV), for building materials as well as other materials of environmental importance.
2. Gamma-spectroscopic analysis techniques used for the determination of 238U, 226Ra, 210Pb, 232Th and 40K in environmental samples, together with the results obtained from the analysis of building materials used in Greece, and industrial by-products used for the production of building materials. Among the techniques used, one is based on the direct determination of 226Ra and 235U from the analysis of the multiplet photopeak at ~186 keV.
3. Results from radon exhalation measurements of building materials such as cement and fly-ash and building structures conducted in the radon chambers in our Laboratory.