石英的顺磁中心在电子自旋共振测年中的特性及应用

Characteristics and Application of Paramagnetic Center of Quartz in Electron Spin Resonance Dating

沉积物的电子自旋共振测年是利用石英矿物中的顺磁中心浓度确定总辐射能量,进而推定石英矿物的埋藏年代。石英中可用于测年的顺磁中心包括E′心、Al心、Ti心和Ge心。E′心需要经过热活化后才能测年。Al心是一种电子空穴心,在低温下可观测到较强的信号值。光照可以使Al心漂白,但有残留值存在。Ti心、Ge心都是电子中心,Ti心在低温测试中可见,信号微弱。Ge心光晒退最敏感,在常温观测中可见。不同顺磁中心的形成机理不同,导致它们具有不同的特性,适用于不同沉积环境中的样品测年,在冰碛物中Ge心测年更具有可行性。电子自旋共振测试时降低温度可使信号增强,Ti心在10 K和15 K时信号强度最大;Al心在20 K时信号最强;Ge心在200 K时信号明显增强。在电子自旋共振测年中可根据不同顺磁中心信号强度的变化调整测试温度获得信号的最优值。在以后的电子自旋共振(ESR)测试中可以选取信号最强时的测试温度进行测试,以增强微弱信号的信噪比,有利于对复杂的信号形态的分辨确定,提高对信号强度定量的准确性。

Electron spin resonance(ESR)dating of sediments is used to determine the total radiation energy by the paramagnetic center concentration in quartz,and then to infer the burial age of quartz minerals.The paramagnetic centers that can be used for dating in quartz include E’center,Al center,Ti center and Ge center.The E’center needs to be thermally activated before it can be dated.The Al center is a kind of electron hole,and its signal can be observed at low temperature.The sunlight can bleach the Al center,but there were residual values.Both Ti center and Ge center are electron centers.The Ti center can be detected at low temperature,but its signal was weak.The Ge center is the most sensitive to sunlight degeneration,which can be detected at room temperature.Different paramagnetic centers have different characteristics due to their different formation mechanisms,which are suitable for sample dating in different sedimentary environments.The Ge center was more feasible for ESR dating in moraine.In ESR test,the signal can be enhanced by reducing temperature.The Ti center signal intensity reached the maximum at 10 K and 15 K.The signal of Al center was strongest at 20 K.The signal of Ge center was significantly enhanced at 200 K.In ESR dating,the temperature can be adjusted according to the change of signal intensity of different paramagnetic centers to obtain the optimal signal value.For the ESR dating in the future,the temperature can be selected when the signal is strongest to enhance the noise ratio of the weak signal in the test,which is conducive to the resolution and determination of complex signal morphology,and the accuracy of signal intensity quantification can also be improved.