Thermoluminescence characterization of natural and synthetic irradiated Ce-monazites

Abstract

The thermoluminescence (TL) emission of synthetic and natural Ce-monazites was characterized here to determine the potential application in the identification of microscopic defects from a qualitative point of view trying to link each TL peak to a chemical-physical process. The kinetic parameters that lead the luminescence processes were calculated by means of variable heating rate and computing glow curve deconvolution methods and allow identifying three groups of components at ∼90, 130 and 290 °C (for the mineral sample) and ∼90, 170, 220, 270 and 320 °C (for the synthetic CePO4:Nd0.20,La0.25). The main differences appreciated in these complex TL curves are mainly due to (i) the content of impurities (natural sample contains lanthanides as well as U 0.60% and Th 5.22%) and (ii) the degree of crystallinity of the samples which is directly related to the type of impurities (synthetic monazite relies only on Nd and La). The behavior of the dose response in the range of 1–8 Gy is similar for both samples; the TL intensity increases linearly as the dose increases without changes in the position of the maxima, denoting first-order kinetic luminescence mechanism. Each peak could be mostly associated with structural defects (i.e., phase transitions), chemical reactions (i.e., Ce3+⇆Ce4+ redox reaction, dehydration or dehydroxylation processes) or intrinsic defects (i.e., Frenkel defects, ODCs or NBOHCs).