Elucidation of the centers responsible for the TL peaks in the anhydride crystal

The mineral anhydride after gamma irradiation displays four thermoluminescence (TL) peaks at 150, 200, 268 and 338 °C. The kinetic parameters, namely activation energy, frequency factor and kinetic order associated with the main TL peaks have been determined using initial rise and glow curve deconvolution (GCD) methods. Defect centers induced in the mineral by gamma irradiation are studied by electron spin resonance (ESR) with a view to identify the centers responsible for the TL process. ESR spectrum at room temperature is observed to be a superposition of at least six defect centers. Center I with principal g-values g_|| = 2.011 and g_⊥ = 2.012 is identified as (SO₄)⁻ radical and the center relates to the TL peak at 200 °C. Centers II, III and IV are characterized by axial g-tensors and all these three centers are assigned to (SO₄)⁻ radicals. These centers correlate with the 268 °C TL peak. Center V with an isotropic g-value equal to 1.9953 is attributed to (SO₃)⁻ radical and the radical is also associated with the 268 °C TL peak. Center VI having an isotropic g factor 2.015 is assigned to an intrinsic O⁻ type center and the center correlates with the TL peak at 268 °C. Center VII displays a rhombic g-tensor and is ascribed to (SO₃)⁻ radical.