Distribution and correlation of the natural radionuclides in a coal mine of the West Macedonia Lignite Center (Greece)

The distribution and correlation of six natural nuclides in the West Macedonia Lignite Center, Northern Greece were studied. Fifty-five samples of lignite, aged from 1.8 to 5 million years, and corresponding steriles, beds of marls, clays and sands alternating with the lignite, were collected perpendicular to the mine benches and measured spectroscopically. The mean concentrations of 238U and 226Ra in lignites were found to be higher than that in steriles since these nuclides are associated with the organic material of lignite, whereas 238U/226Ra equilibrium was not observed in either lignites or steriles. Finally, the ratio 226Ra/228Ra in lignites was approximately double of that in steriles, confirming the affinity of the 238U series with the coal matrix in contrast to the 232Th series. No correlation was found between radionuclide concentrations and the depth of the sample, nor with the ash content of lignite.