熱ルミネッセンス法による第四紀酸性火砕流及び火山岩の年代測定  [in Japanese] Thermoluminescence dating of acidic pyroclastic flows and lavas in Quaternary age  [in Japanese]

Thermoluminescence (TL) dating is applied to 8 volcanic rock samples collected from the Noboribetsu, Hachimantai and Onikobe areas. A mineral used for TL dating is quartz phenocryst with the size of 2 to 6 mm in diameter. It is assumed that the contributions of beta rays were zero or negligible because the size of quartz phenocryst was large. The obtained TL ages of 8 samples range from 0.038 to 1.69 Ma which correspond with the ages obtained from other methods and stratigraphical evidences. In TL dating, there is no problem for quartz separation with chemical treatments, gamma rays irradiation processes and glow measurements. The errors caused by the above mentioned experiments are estimated less than 5%. However, the errors for chemical analyses of U and Th are 5 to 10 % or more, and directly related to errors of TL age. Thus, total errors on TL dating range from 6 to 13 %, and most of them come from uncertainty of U and Th analyses. The problem still remains in TL dating of volcanic rocks. The biggest is a way of evaluation of annual dose rate, especially the counting of beta rays contributions.