Search Results (3)

The present work aims to analyze the distribution of radionuclides naturally occurring in the oil shale of the Ama Fatma coastal zone. For this purpose, using gamma-ray spectrometry, we analyzed the activity concentrations of uranium (U), thorium (Th) series, and potassium-40 (K-40) in oil shale samples retrieved from the study area. The concentrations of U-238 ranged from 45 ± 36 to 194 ± 50 Bq.kg⁻¹ and those of Th-232 fluctuated between 1.48 ± 0.92 and 9.47 ± 1.06 Bq.kg⁻¹. The measured concentrations for Ra-226, Pb-214, and K-40 oscillated between 33 ± 5 and 138 ± 9 Bq.kg⁻¹, 18 ± 1 and 68 ± 3 Bq.kg⁻¹, and between 17 ± 4 and 279 ± 16 Bq.kg⁻¹, respectively. The obtained values variation appears to be related to the deposit nature and assimilation processes of appropriate radionuclides rather than the retrieved samples’ related depth. The analysis of ²³²Th/²³⁸U and ²²⁶Ra/²³⁸U allowed an understanding of these radionuclides’ behaviors. The ratios ²²⁶Ra/²³⁸U ranged from 0.56 to 0.74 with a mean value of 0.70 which indicates the existence of disequilibrium in the investigated oil shale samples. This disequilibrium can be attributed to significant differences in the mobility of these radionuclides. Full article

There are many regulations related to the radiological control of NORMs (Naturally Occurring Radioactive Materials) in activities such as mining, industry, etc. Consequently, it is necessary to apply fast and accurate methods to measure the activity concentrations of long-lived natural radionuclides (e.g., ²³⁸U, ^{234,232,230,228}Th, ^228,226Ra, ²¹⁰Pb, ²¹⁰Po, and ⁴⁰K) in samples characterized by a wide variety of compositions and densities, such as mining samples (wastes, minerals, and scales). Thus, it is relevant to calculate the radioactive index (RI), which summarizes for all radionuclides the ratio between the activity concentration and its respective threshold activity concentration as established by regulations, in order to classify a material as a NORM. To proceed with the determinations of these radionuclides, two spectrometric techniques based on both alpha-particle and gamma-ray detections should be employed. In the case of gamma-ray spectrometry, it is necessary to correct the full-energy peak efficiency (FEPE) obtained for the calibration sample, ${\epsilon }_c$, due to self-attenuation and true coincidence summing (TCS) effects. The correction is especially significant at low gamma emission energies, that is, $E_{\gamma }$ < 150 keV, such as 46 keV (²¹⁰Pb) and 63 keV (²³⁴Th). On the other hand, in samples which contain radionuclides that are in secular disequilibrium with others belonging to the same series (²³⁸U or ²³²Th series), like wastes or intermediate products, it is necessary to measure some pure-alpha emitters (²³²Th, ²³⁰Th, ²¹⁰Po) by employing alpha-particle spectrometry. A practical and general validated procedure based on both alpha and gamma spectrometric techniques and using semiconductor detectors is presented in this study. Full article

Uranium (U) concentration and the activities of ²³⁸U, ²³⁴U, and ²³⁰Th were determined for groundwaters, spring waters, and lake water collected from the Shihongtan sandstone-hosted U ore district and in the surrounding area, NW China. The results show that the groundwaters from the oxidizing aquifer with high dissolved oxygen concentration (O₂) and oxidation-reduction potential (Eh) are enriched in U. The high U concentration of groundwaters may be due to the interaction between these oxidizing groundwaters and U ore bodies, which would result in U that is not in secular equilibrium. Uranium is re-precipitated as uraninite on weathered surfaces and organic material, forming localized ore bodies in the sandstone-hosted aquifer. The ²³⁴U/²³⁸U, ²³⁰Th/²³⁴U, and ²³⁰Th/²³⁸U activity ratios (ARs) for most water samples show obvious deviations from secular equilibrium (0.27–2.86), indicating the presence of water-rock/ore interactions during the last 1.7 Ma and probably longer. The ²³⁴U/²³⁸U AR generally increases with decreasing U concentrations in the groundwaters, suggesting that mixing of two water sources may occur in the aquifer. This is consistent with the fact that most of the U ore bodies in the deposit have a tabular shape originati from mixing between a relatively saline fluid and a more rapidly flowing U-bearing meteoric water. Full article