Study on absolute age determination for inland clastic sediments, especially on dosimetric dating

本研究的主要目的是建立一种在没有任何晚第四纪年代标志化石的情况下确定非海相碎屑沉积物中晚更新世年龄的方法。主要测试了典型的内陆沉积物，包括火山灰、风成黄土、淡水硅藻土和河湖沉积物。利用热释光（TL）和电子自旋共振（ESR）技术观测剂量信号，测量沉积后的古剂量积累。剂量学：石英或硅玻璃纯化后，用6-12MeV直线加速器的电子束或x射线照射样品。一些样品在辐照前进行了退火，以评估剂量饱和度。采用TL探针原位剂量测定法和伽玛能谱法化学数据活度估算法测定年剂量率。对23个样品进行了剂量测年试验。其中，半数标本的年代在10Ka ~ 700Ka B.P.之间（Ka =10^3年）。由于剂量几乎完全饱和，一些样品未能得到它们的沉降年龄。因此，本文提出了以下问题和意见：(1)含石英沉积物最适合于基于日光破坏（时间归零）和结晶机制的剂量测年。(2)火山玻璃和硅藻土等非晶态试样，如果在辐照过程中避免饱和，可以在液氮温度下采用低功率ESR测定年代。(3)超过4.5 Gray/min的高剂量率照射会改变敏感性和/或敏感性，特别是在大多数年龄大于100Ka的样品中。(4)直线电子束（或x射线）源辐照由于其剂量控制精度高而非常有用。(5)精密伽马射线探测器可用于直接测量天然放射性元素（U、Th、K）的剂量率和定量分析。少

Main aim of this study is to establish a method for the Mid to Late Pleistocene age determination of non-marine clastic sediments without any chronological marker fossils for the later Quaternary. Typical inland sediments including volcanic ash, eolian loess, fresh water diatomite, and river and lake deposits are mainly tested. Paleodose accumulated after sedimentation were measured by means of dosimetric signals observed by using thermoluminescence (TL) and electron spin resonance (ESR) techniques.Dosimetry: After purification for quartz or silica glass, those samples were irradiated by electron beam or X-ray from 6-12MeV linear accelerator. Some samples were annealed before irradiation in order to evaluate saturation in dose. Annual dose rate were measured by using two methods, in-situ dosimetry using TL probes and activity estimation from chemical data of gamma-ray spectrometry.Experiments for dosimetric dating of 23 specimens was conducted. Among these, a half specimens were succes … More sfully dated ranging from 10Ka to 700Ka B.P. (Ka =10^3 years). Because of almost complete saturation in dose, several samples were failed to get their ages of sedimentation.Consequently, the following topics and comments are pointed out: (1) Quartz bearing sediments would be most suitable for the dosimetric dating based on a mechanism of sun-light breaching (time zeroing) as well as that of crystallization. (2) Amorphous specimens such as volcanic glass and diatomite could be dated by using low power ESR measurement at liquid nitrogen temperature, if saturation were avoidable during irradiation. (3) High dose rate irradiation over 4.5 Gray/min would change susceptibility and/or sensitivity especially in cases of most sample older than 100Ka. (4) Irradiation by means of lineac electron beam (or X-ray) source is very useful because of its high accuracy of dose control. (5) Precise gamma-ray detector can be put to practical use for direct measurement of dose-rate as well as quantitative analysis for natural radioactive elements (U,Th,K). Less