Low-magnesium uranium–calcite with high degree of crystallinity and gigantic luminescence emission

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• 作者：Francisco-Jose Valle-Fuentes ; Javier Garcia-Guinea ; Ana Cremades ; Virgilio Correcher ; Sergio Sanchez-Moral ; Rafael Gonzalez-Martin ; Luis Sanchez-Muñ ; oz ; Paula Lopez-Arce
• 关键词：Low-magnesium ; Uranium– ; calcite ; Thermoluminescence ; Cathodoluminescence ; X-ray diffraction
• 刊名：Applied Radiation and Isotopes
• 出版年：2007
• 期刊代码：6_09698043
• 类别：ce
• 出版时间：January 2007
• 卷：65
• 期：1
• 页码：147-154
• 文件大小：419 K

摘要

Cabrera (Madrid) low-Mg calcites exhibit: (i) an unusual twofold elevation in X-ray diffraction pattern intensity; (ii) a 60-fold elevation of luminescence emission, compared to six common natural calcites selected for comparison purposes; (iii) a natural relatively high radiation level of circa 200 nSv h⁻¹ not detected in 1300 other calcites from the Natural History Museum of Madrid. Calcites were analysed by the X-ray diffraction powder method (XRD), cathodo-luminescence spectroscopy in scanning electron microscopy (CL-SEM), thermoluminescence (TL), differential thermal analysis (DTA), X-ray fluorescence spectrometry (XRF) and particle size distribution (PSD). The Cabrera calcite study shows: (i) helicoidally distributed steps along the (0 0 0 1) orientation; (ii) protuberance defects onto the (0 0 0 1) surface, observed by SEM; (iii) XRF chemical contents of 0.03%MgO, 0.013%of Y₂O₃, and 0.022%of U₃O₈, with accessory amounts of rare earth elements (REE); (iv) DTA dissociation temperature of 879 °C; (v) TL maxima peaks at 233 and 297 °C whose areas are 60 times compared to other calcites; (vi) spectra CL-SEM bands at 2.0 and 3.4 eV in the classic structure of Mn²⁺ activators; (vii) a twofold XRD pattern explained given that sample is a low-Mg calcite. The huge TL and CL emissions of the Cabrera calcite sample must be linked with the uranyl group presence. This intense XRD pattern in low-Mg calcites could bring into being analytical errors.