Yuanzineng kexue jishu (Feb 2024)
Thermoluminescence Characteristics of Sandstone-type Uranium Deposit Soil and Optimization of Measurement Process
Abstract
As a technique in the measurement of accumulated radon for uranium resource exploration, the natural soil thermoluminescence method is widely applied in the exploration of sandstone-type, granite-type, and volcanic rock-type uranium deposits, and achieves good results in Inner Mongolia, Jiangxi, Hunan, and other places, and delineates the spatial distribution of concealed uranium deposits in geological bodies. However, the natural soil thermoluminescence method often uses the thermoluminescence signal corresponding to the entire soil for soil thermoluminescence measurement, which may result in the inclusion of unstable luminescence signals with severe abnormal attenuation in the thermoluminescence signal of the entire soil, thereby reducing the resolution of the natural soil thermoluminescence method for weak abnormal information of deep uranium deposits. In this study, thermoluminescence analysis was carried out on soil samples from sandstone-type uranium deposits in the Qinghai Qaidam Basin (QH sample) and the Ordos Basin (TL sample). The distribution of luminescence signals under different pre-processing stages was obtained, and the luminescence signals of the main mineral components (Na2CO3, MgCO3, orthoclase, NaHCO3, albite, CaCO3, quartz) in the soil samples were reconstructed using the computerized glow curve deconvolution method, in order to further clarify the accurate sources of the changes in the TL signals under different pre-processing stages. In order to analyze the sources of unstable TL signals in soil samples, four different storage time (0, 20, 40, and 60 h) was set after irradiation, and the next measurement step was done after the storage time was reached. It is found that the temperature range where stable TL signals existed is between 200-400 ℃ and the TL decay curve is basically stable at a time interval of 60 h. By comparing the TL decay curves measured after preheating and infrared excitation with the TL decay curve measured under the 60 h time interval, it is found that the luminescence signals obtained after preheating and infrared excitation meet the requirements of luminescence measurement. Based on this, an optimized measurement process for thermoluminescence applicable to sandstone-type uranium deposits is proposed and validated. The process is aimed at the mixed mineral composition of feldspar and quartz, and its selected TL signal has better dose response characteristics in the range of 0-600 Gy irradiation dose, and the relative error of the equivalent dose measurement value is less than 7%, so the process takes into account the measurement efficiency and accuracy, and it provides technical references for the application of natural soil pyrophotography in the exploration of sandstone-type uranium deposit.
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