Artificial optical bleaching of the Aluminium center in quartz implications to ESR dating of sediments
Artificial optical bleaching of the Aluminium center in quartz implications to ESR dating of sediments
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DOI：
10.1016/s0277-3791(03)00062-3
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发表时间：
2003-05
影响因子：
4
通讯作者：
P. Voinchet;C. Falguères;M. Laurent;S. Toyoda;J. Bahain;J. Dolo
中科院分区：
文献类型：
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作者：
P. Voinchet;C. Falguères;M. Laurent;S. Toyoda;J. Bahain;J. Dolo
从沉积物中提取的石英的电子自旋共振(ESR)测年可能有助于阐明新近纪和第四纪的年代地层学，特别是在不能应用热释光或K/Ar等方法的亚热带沉积物中。ESR方法适用于风成、滨海和河流沉积，当石英被光学现象(在这种情况下主要是由于紫外线太阳光的光电效应)而归零或漂白时。漂白石英的ESR测年是基于晶格中顺磁性取代原子的存在。铝中心可以被光学漂白，其在化石样品中的信号强度比暴露在太阳光下的信号强度要低。经过很长一段时间，ESR强度达到一个平台值，对应于不能被光能“提取”的电子。这些电子代表“剩余”剂量，必须从总的当量剂量中减去，才能得到考古剂量。我们的动力学研究的目标是获得一个新的模型化，并建立一个正确的自然漂白时间，以使用适当的石英样品进行测年。我们调查了来自克鲁斯河阶地系统(法国)的一块河沙化石。我们得到的实验漂白曲线与Walther和Zilles(Quat.SCI。Rev.13(1994)611)。
Electron spin resonance (ESR) dating of quartz extracted from sediments may contribute to elaborate a Neogene and Quaternary chronostratigraphy, especially in the case of azoic deposits, when methods such as thermoluminescence or K/Ar cannot be applied. The ESR method is applicable for aeolian, littoral and fluvial sediments when quartz is zeroed or bleached by an optical phenomenon (photoelectric effect due mainly to UV solar rays in this case). ESR dating on bleached quartz is based on the presence of paramagnetic substituted atoms in the crystal lattice. The Al-center can be optically bleached, and its signal intensity decreases in fossil samples versus exposure to the solar light. After a long time, the ESR intensity reaches a plateau value corresponding to the electrons which cannot be “extracted” by the light energy. These electrons represent a “residual” dose which must be subtracted from the total equivalent dose in order to obtain the archaeological dose. Our kinetic study has the objectives of obtaining a new modelization and to establish a correct time of natural bleaching for using quartz sample as appropriate for dating. We have investigated samples from a fossil fluvial sand from the Creuse river terraces system (France). Our experimental bleaching curve obtained is compared with that one previously proposed by Walther and Zilles (Quat. Sci. Rev. 13 (1994) 611).