The Analysis of Influence Factors on Electron Spin Resonance Signal Intensity in Dating of Quartz in Fault Lines

Electron Spin Resonance (ESR) is a dating technique using the accumulated irradiation energy in minerals under geological environments as the target. The quartz used for isotopic dating is widely distributed, and has an excellent time starting point to record fault deformation. This implies that ESR will become a valuable supplement to isotopic dating. ESR signal intensity is the key factor affecting the accuracy of ESR age, but the influence pattern and degree of different parameters on ESR signal intensity remains unknown. A paramagnetic E' center in quartz from fault zones was taken as the main investigation object. By single factor repeated experimental method, the relationship between 5 parameters of ESR dating and ESR signal intensity was analyzed. The results indicate that microwave power, field modulation amplitude, and scan width are the most important factors affecting ESR signal intensity, however the inserted direction and diameter of the sample tube had a slight influence on measuring the data. The microwave power from 0.02 mW to 0.1 mW (in Fig.1), and the field modulation amplitude from 0.25 Gs to 0.4 Gs can be used as a universal parameter range to precisely measure E' center in fault clay quartz (in Fig.3). Improper scan width was unsuitable for ESR measuring. Before the fine scanning, the pre-scan should be performed under wider scan width and then the proper scan width can be identified. Calculating the average value based on repeated measuring data can help to decrease measurement error effectively. When the proposed parameter range and measuring method are used to measure the E' center signal intensity of fault clay quartz, the ESR measurement precision can be improved remarkably.