Thermal stability of artificial radiation-induced defects in kaolinite: Enhancing EPR dating protocol

Abstract

Kaolinite naturally contains radiation-induced electron defects in its structure induced by ionizing radiations and can be analyzed with electron paramagnetic resonance spectroscopy (EPR). They include the so-called A-center, which is crucial for geochronological applications due to its stability at the scale of geological periods. Indeed, previous studies have substantiated the thermal stability of naturally occurring A-centers in kaolinite through annealing experiments. However, the stability of artificially created A-centers, which are used to determine paleodose through calibration via irradiation experiments and subsequent dating of kaolinite formation, still needs to be more adequately specified to confirm their relevance. Therefore, this research probed the thermal stability of A-centers produced by ionizing 1.5 MeV He+ beams in two samples, i.e., the reference KGa-2 and a very disordered lateritic soil kaolinite. Heating experiments showed that the annealing of irradiated samples at 250 °C was relevant to determining A-center concentration. Second, the annealing of artificial A-centers at higher temperatures was found to be a second-order process, as for natural A-centers. Annealing parameters such as activation energy (2–2.6 eV) were determined with estimates of half-life at 300 K, which was found to be >1012 years for natural and artificial A-centers. Thus, the parameters for artificial A-centers are consistent with the thermal annealing behavior of their natural counterparts. These new findings affirm that artificially generated A-centers mimic natural ones in terms of EPR spectra and thermal stability, enhancing the reliability and precision of the EPR dating methodology used in kaolinite dating.