The thermal stability of radiation-induced defects in illite

High-purity illite specimens from the Mesoproterozoic unconformity-related uranium deposits of Kiggavik, Thelon basin, Nunavut (Canada), and Shea Creek (Athabasca basin, Saskatchewan, Canada) have been studied using electron paramagnetic resonance spectroscopy to determine the thermal stability of the main radiation-induced defects and question the potential of using illite as a natural dosimeter. The observed spectra are complex as they can show in the same region several contributions: (1) an unstable native defect, (2) the main stable defect named Ai by reference to a previous study (Morichon et al. in Phys Chem Minerals 35:339–346, 2008), (3) a signal at g = 2.063 assigned to a new defect, not yet fully characterized, named Ai2 center and (4) impurities such as vanadyl complex or divalent manganese. Isochronal heating shows that the new signal corresponds to a stable species. Isothermal heating experiments at 400 and 450 °C provide values of half-life extrapolated at room temperature and activation energy of 1.9–29,109 years and 1.3–1.4 eV, respectively, corresponding to the Ai center. These parameters allow the use of stable radiation-induced defects as a record of radioactivity down to the Paleoproterozoic period.