Thermoluminescent mechanisms of gamma irradiated calcium sulfate doped with dysprosium

Thermoluminescent (TL) mechanisms of CaSO4:Dy caused by exposure to ionizing radiation are investigated. Intrinsic and extrinsic defects in irradiated CaSO4:Dy are observed and identified using electron spin resonance (ESR) and optical absorption techniques. These defects are then followed with ESR through a series of isochronal heat treatment which allow the correlation of specific defects with the glow curve structure. Influences of the monovalent and tetravalent impurities on the structure of the glow curve are determined and related to the concentration of calcium vacancy in the CaSO4 crystal structure. Thermally stimulated current (TSC) studies are performed to determine the TL process as bimolecular or monomolecular. The information from these studies is combined to form comprehensive models of the TL mechanisms responsible for the TL glow peaks occurring in CaSO4:Dy between room temperature and 4000C. The glow peak occurring between 150 and 2600C, usually designated as the dosimetric peak, was determined to be the result of the decay of four different calcium vacancy two-hole trap centers. In the vicinity of 2000C, these two-hole vacancy centers release their first hole; the second hole is not released until a higher temperature is reached