Radiation Protection Dosimetry · 1986 · 34 citations · 0 references
Natural SciencesChemistryMaterials ScienceCrystal StructureInorganic ChemistryPhysical ChemistryCrystal ChemistryCrystallographyCrystal Defects During GrowthDefect Evolution Under IrradiationImpurity DefectsIntrinsic DefectsParamagnetic CentersParamagnetic SpeciesRadiation Defect CharacterizationThermoluminescent Materials
Abstract ESR studies of gamma-irradiated CaSO4:Dy have shown, in addition to the usual intrinsic defects, four new paramagnetic centres. An analysis of the g values and the g tensors in conjunction with the anhydrite crystal structure indicate that these centres are related to sulphate ions, this structure being stabilised by a neighbouring Ca vacancy. Centre 3b is suggested as a hole associated with one sulphate ion, again stabilised by an adjacent Ca vacancy. Because of the two distinct crystallographic directions in the anhydrite structure, centre 3b was found to consist of two distinguishable defects with slightly differing decay temperatures. The fourth centre appears to be an electron trapping site with structure similar to centre 3b. Decay temperatures of these ESR defects are correlated with the observance of TL peaks in CaSO4:Dy. Thermoluminescence studies as a function of impurity content confirmed the presence of calcium vacancies, which are formed during crystal growth, and that they play an important role in the TL process. TL models are proposed to account for the observed properties of CaSO4:Dy.