[S-GL30] 地球年代学・同位体地球科学

[SGL30-03] 石英のESR信号の自然・人為放射線応答曲線の比較

*塚本 すみ子¹、Long Hao²、Richter Marcus¹、Li Yan¹、King Georgina³、He Zhong⁴、Yang Linhai⁵、Zhang Jingran⁶ (1.Leibniz Institute for Applied Geophysics、2.Nanjing Institute of Geography and Limnology, Chinese Academy of Science、3.University of Bern、4.Northwest A&F University、5.Northwest Institute of Eco-environment and Resources, Chinese Academy of Science、6.Nanjing Normal University)

キーワード：ESR年代測定、石英、線量応答曲線、中国レス

The natural electron spin resonance (ESR) dose response curve (DRC) of the Al and Ti centres was constructed for the first time using sand-sized quartz samples from Luochuan, Chinese Loess Plateau, to investigate the upper limit of quartz ESR dating. The natural DRC of both centres showed an unexpected early saturation, with characteristic saturation dose (D₀) values of 770 Gy for the Al centre and 650 Gy for the Ti centre. This corresponds to the upper age limit of ~500 ka (Al centre) and ~400 ka (Ti centre), using the mean dose rate of 3 Gy/ka. The regenerated laboratory DRC of both centres showed much higher saturation dose, but both the intensity and D₀ value of the regenerated ESR signals decreased significantly with increasing preheat temperatures. The natural DRC had a better match with the laboratory DRC following higher temperature preheats, ~210-240°C for 4 minutes, clearly indicating the need for preheating after laboratory irradiation for quartz ESR dating. The results of isothermal heating tests revealed that the thermal lifetime at 10°C at the studied site was 1.5 x 10⁹ and 1.7 x 10⁶ years for the Al and Ti centres respectively. The relatively short thermal lifetime of the Ti centre may explain the early saturation of the natural Ti DRC. The thermal stability of ESR signals plays an important role in controlling the maximum dating range of ESR.