Dose dependence of the thermoluminescence (TL) peak at 200 K in AlNa containing quartz crystals

Abstract

The 200 K thermoluminescence (TL) peak in the AlNa containing quartz is related to [SiO 4/Na] 0 centers. The production of these centers generally involves a double excitation [Halperin A. and Katz S., J.Lwninesc. 31/32, 129 (1984)]. In preliminary experiments the dose dependence curves were found to exhibit varying slopes and shapes. These variations were traced back to variations in the competition for electrons between the [SiO 4/Na] + traps and other electron traps depending on previous heat and irradiation history. To better understand this process, measurements were carried out under controlled conditions which separated the effects of the first and second excitations. This resulted in simple dose dependence curves. The first excitation (and suitable wanning when needed) provides the [SiO 4/Na] + traps. The second irradiation provides electrons which, when captured by [SiO 4/Na] + traps, produce the [SiO 4/Na] 0 centers. With the second irradiation remaining fixed, the slopes of the curves describing the 200 K TL intensity as a function of the time of the first irradiation gave slopes from 0 up to 1. Just a few seconds of the first excitation were found to release a high percentage of the available Na ions from the Al. With the first irradiation fixed, and preventing changes in the competition for electrons, the dose dependence of the 200 K TL peak as a function of the second excitation gave a slope of one up to the saturation of the [SiO 4/Na] + traps. Varying both the first and second exposure times gave slopes up to 2. At very intense excitations (long exposures) the 200 K TL peak decreased in intensity. This seems to have resulted from trapping of some of the Na ions at defects in the quartz lattice stable up to above 400 K and thus lost for the production of the [SiO 4/Na] + traps related to the 200 K TL.