Radiometric, SEM and XRD investigation of the Chituc black sands, southern Danube Delta, Romania

Abstract

The black sand of the Chituc marine sand bank, northern of the city of Navodari (Romania), presents anomalous high radioactivity. Field measurements recorded in some places dose rate up to 200 nSv/h, significantly overpassing the average value of 44 ± 20 nSv/h along the entire Southern sector of Romanian Black Sea shore.Gamma ray spectrometry performed on both Slanic-Prahova Underground Low Background Laboratory and Geological Institute of Romania Radiometric Facilities showed with clarity the dominance of 228Ac radioisotope in the 50 microns fraction together with the 226Ra and traces of 40K. No significant amount of anthropogenic 137Cs was identified.Based on radiometric as well as on SEM–EDAX and XRD determinations we come to the conclusion that the evidenced radioactivity could be attributed to both uranium and thorium series in the zircon and monazite fractions and to a lesser extent to potassium in the feldspars.