Dating of Quaternary with ESR, TL and OSL methods : intercomparison

基于相同原理的ESR（电子自旋共振）、TL（热释光）和OSL（光激发光）测年方法在第四纪年龄测定方面有着比放射性碳法更广泛的应用。然而，这些仍然被认为是可行的方法。在本项目中，这三种方法应用于不同已知年龄的相同火山灰样本，以便获得的年龄可以相互比较，也可以与已知年龄进行比较。 Tepharas 也是本项目中的合适样本，因为它们是许多地质环境中的重要关键层。石英颗粒提取自 Zenigame-Menakawa、Shibahara、Shirakawa-Ten'ei、Shirakawa-Saigo、Nantai-Shichihonzakura、Ikedako、Irito Aira-Tanzawa (Irito Ignimbrite)、Aira-Shiko、Aira-Iwato、 Kikai-Kuzuhara、Ata-Torihama、Kuju-1、Kuju-Handa 和 AT tephras。通过ESR和等温TL方法获得自然累积剂量。本研究发现，OSL 不适合测量日本火山灰，因为恢复率太大，无法获得可靠的累积剂量。自然剂量率是通过低背景伽马射线能谱测量的样品中的U、Th和K浓度获得的。等温TL年龄与已知年龄一致，而ESR年龄在100ka以下范围内没有那么不一致，但有时年龄较大的样品中年龄非常分散。问题可能应该是附加剂量方法，其中将伽马射线剂量应用于样本以观察信号强度的增加，并将信号强度外推到零纵坐标以获得自然累积剂量。进行了信号再生的初步实验，发现该协议的统计误差变得更小。

ESR(electron spin resonance), TL(thermoluminescence), and OSL(optically stimulated luminescence) dating methods, based on the same principle, have wide applications of age determination in quaternary in the range beyond that of radiocarbon method. However, these have still been considered to be viable methods. In the present project, these three methods were applied to the same tephra samples of various known ages so that the obtained ages can be compared with each other, also with the know ages. Tepharas are also appropriate samples in the present project in the aspect that they are important key layers in many geological contexts.Quartz grains were extracted from Zenigame-Menagawa, Shibahara, Shirakawa-Ten'ei, Shirakawa-Saigo, Nantai-Shichihonzakura, Ikedako, Irito Aira-Tanzawa (Irito Ignimbrite), Aira-Shiko, Aira-Iwato, Kikai-Kuzuhara, Ata-Torihama, Kuju-1, Kuju-Handa, and AT tephras. Natural accumulated doses were obtained by ESR and isothermal TL methods. It was found in the present study that OSL is not appropriate for measurement of Japanese tephras because the rate of recupelation is too large to obtain reliable accumulated doses. Natural dose rates were obtained from the concentrations of U, Th and K concentrations in the samples which were measured by the low background gamma ray spectroscopy.Isothermal TL ages were consistent well with the known ages while ESR ages are not so much inconsistent in the range younger than 100ka, but sometimes the ages were so much scattered in the samples of older ages. The problem should probably be the additive dose method where the gamma ray dose were applied to the samples to see the increase of the signal intensities which are extrapolated to the zero ordinate to obtain natural accumulated doses. Preliminary experiments on signal regeneration were performed to find the statistical errors become much smaller with this protocol.