Natural Radioactivity of Felsic Rocks of the Archaean Granite Greenstone Terrane of Bulawayo, Zimbabwe Craton

Abstract This study investigates the natural radioactivity and associated radiological hazards of felsic rocks in the Archaean Granite Greenstone Terrane of Bulawayo (AGGTB), Zimbabwe Craton. Firstly, the activity concentrations of the 238 U decay series, 232 Th decay series, and 40 K non series radionuclides in twenty four (24) representative felsic rock samples collected from the three main exposed felsic rock units in the AGGTB, namely younger porphyritic granites, fenitised granites and older gneissic granites were determined using a High Purity Germanium (HPGe) gamma-ray spectrometry detector system. Subsequently, the radiological hazard parameters quantifying the associated radiation exposure of its inhabitants to the 238 U decay series, 232 Th decay series and 40 K non series radionuclides within the exposed felsic rock units in the AGGTB were computed. The mean activity concentrations for the 238 U decay series, 232 Th decay series and 40 K non series radionuclides for the younger porphyritic granites were found to be 177.885 ± 0.009 Bq/kg, 252.261 ± 0.021 Bq/kg and 1422.178 ± 0.071 Bq/kg, respectively. The mean activity concentrations for the 238 U decay series, 232 Th decay series and 40 K non series radionuclides for the fenitised granites were found to be 137.788 ± 0.007 Bq/kg, 253.724 ± 0.021 Bq/kg and 1799.935 ± 0.087 B/kg, respectively. The mean activity concentrations for the 238 U decay series, 232 Th decay series and 40 K non series radionuclides for the older gneissic granites were found to be 40.889 ± 0.003 Bq/kg, 102.698 ± 0.009 Bq/kg and 1175.093 ± 0.063 Bq/kg, respectively. These results show that the natural radioactivity in the AGGTB, particularly in areas underlain by both the younger porphyritic granites and the fenitised granites may pose some radiological health risks to its inhabitants.