Estimation of terrestrial gamma radiation (TGR) dose rates in characteristic geological formations of Jos Plateau, Nigeria

A study was conducted to estimate the terrestrial gamma radiation (TGR) dose rates due to the natural radionuclides U-238, Th-232 and K-40 in the characteristic geological formations of Jos Plateau. A total of 51 surface soils samples from all the geological units were collected and measured using high-resolution gamma ray spectrometry system. From the measured activity concentrations of U-238, Th-232 and K-40, TGR dose rates in air outdoors 1 m above the ground surface, were estimated to be in the range of 36 nGy h(-1) to 456 nGy h(-1), depending on the geological formation, with an overall mean value of 143 nGy h(-1). The estimated mean value is by a factor of two higher than the world average value of 59 nGy h(-1). Geological formation G8 (younger granites) appeared to have the highest mean TGR dose rate while G7 (sandstone, clay and shale) show the lowest mean TGR dose rate. The results of this study inferred that, TGR dose rates outdoors for Jos Plateau varies with the diversity of geological formations and is significantly contributed by Th-232. An isodose map for TGR dose rates due to natural sources was also plotted using ArcGIS software. The data here presented can be used to evaluate public radiation dose and can be useful for geochemical exploration.