Measurements of Radioactivity Concentrations in Granites and Sedimentary- Rocks and their Leaching Components in Egyptian Deserts

Abstract

Concentrations of radionuclides in sediments and granite samples were determined by γ- ray spectrometer using High Pure Germanium Detector; HPGe, with a specially designed shield. Six different rock samples were collected from different sites: four samples of sediments from Um Bogma southwest Sinai, and two granite samples from Gabal Gattar, the northern part of the East- ern Desert of Egypt, where all samples were subject to investigation. Their samples were selected because the activity before being dissociated in sulfuric acid was less than after dissociation. The samples were dissolved in sulfuric acid with the same parameters of solid to liquid ratio; S/L, acid concentration, and leaching time. After the leaching process, the pregnant solution was separated from the residual, and the latter was dried. The two units, named the pregnant solutions and residu- als, were also measured radiometrically using the HPGe detector to determine the activity concen- trations (Bq/kg) of the different radionuclides of the six samples. The results showed that the rela- tion between the sum of activities of both pregnant solutions and residuals with the originals have different categories. In the sediment samples; the activity of solution+ residual was 72.37% from the original of siltstone, the activity of solution + residual was 90.02% from the original claystone sample, the activity of solution + residual was 92.6% from the original of shale, the activity of solu- tion + residual was 74.07% from the original claystone. In the granite samples, the activity of solu- tion + residual was 130.39% from the original of the first granite sample and 142.3% from the orig- inal of the second granite sample. This phenomenon varied in magnitude due to the different radio- nuclides in each sample. These variations depend mainly on the nature of the grain surfaces in the different rock types and their Pb content. As for leachability analysis, leaching experiments have been performed using sulfuric acid. The leaching efficiency (%) of uranium is estimated by the measurements of the HPGe detector. The result showed almost constant values for leachability. The non-frequent appearance of attenuation of gamma activities during leaching processes indicates that the acid solutions may have led to clean the grain surfaces and thus permit gamma activities of the inner grains to be measured. The treatment of the samples before measurements may have been needed.