Electron Spin Resonance (ESR) Signal Analysis of Fossil Teeth from Mae Moh Mine, Thailand

This study investigates the characteristics of Electron Spin Resonance (ESR) signals in fossil tooth enamel collected from the Mae Moh lignite mine in Lampang Province, Thailand. ESR spectra were recorded at room temperature (298 K) using a Bruker EMX Premium spectrometer operating at X-band (9.85 GHz) with a modulation frequency of 100 kHz and a modulation amplitude of 0.3 mT. The most prominent signal was observed at g ≈ 2.002, attributable to trapped carbonate radicals within the hydroxyapatite crystal lattice. By applying the Multiple-Aliquot Additive Dose (MAAD) protocol, the ESR intensity at g ≈ 2.002 exhibited a strong linear relationship with laboratory-administered gamma doses (0–2000 Gy), yielding a dose-response slope of 0.2185 a.u./Gy (R2 = 0.907). From this calibration, the natural accumulated dose for the fossil teeth was determined to be 550 ± 30 Gy. These findings demonstrate the reliability of ESR signal analysis for quantifying accumulated radiation dose in fossil enamel and support its application for future geochronological investigations in the Mae Moh basin.