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

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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