Mechano and thermoluminescence of gamma-irradiated CaSO4:Dy phosphor

In order to have a better idea of the interaction of the defect centres produced by y-irradiation with dislocation in the processes of deformation destruction, mechanoluminescence (ML) and thermoluminescence (TL) of gamma-irradiated CaSO4:Dy, these phosphors have been investigated. CaSO4:Dy phosphors were prepared by dissolving CaSO4.2H2O in sulphuric acid and evaporating the excess acid around 300 degrees C. ML was excited impulsively by dropping a load on to the sample. Two peaks have been observed in the ML intensity against time curve. The total light output, i.e. integrated ML intensity, increases with concentration of dopant, strain rate and with irradiation doses. The TL glow curves of CaSO4:Dy phosphors at different concentrations of dopant and irradiation doses were also recorded. Studies of the influence of post-irradiation annealing on the ML of CaSO4:Dy show that with the removal of the TL dosemetric peak (approximately 210 degrees C) the ML intensity decreases markedly. A spectroscopic study of ML and TL has also been carried out to elucidate the mechanism of ML. Correlation between ML and TL has also been found.     

Thermoluminescence characteristics of teflon embedded CaSO4:Dy TLD

The Korea Atomic Energy Research Institute (KAERI) is manufacturing CaSO4:Dy Teflon TL pellets which have more sensitivity and stability than commercial TLD. A method is presented of preparing the CaSO4:Dy phosphor-embedded Teflon powder, which is then compressed to a thin pellet form used as the TLD element. Investigations are made to determine optimum preparation conditions and dosimetric characteristics of the CaSO4:Dy Teflon pellet such as the sensitivity, energy response, dose response, fading, re-usability, and lowest level of detection. The results show that the sensitivity of the CaSO4:Dy pellet is 2 times higher than that of the commercial Teledyne CaSO4:Dy pellet. A dose-response was observed to be linear in the range from 10(-5) to 10 Gy. The relative energy response in the low energy region was 9.6 (normalised to the 137Cs gamma source), and the fading rate was about 10% for five months. The re-usability was estimated to be more than 60 cycles, and the low level of detection dose was 22 microGy. From the results, the CaSO4:Dy pellet developed in KAERI can be successfully used in personal dosemeters through appropriate filter design for compensating the energy response.     

Defect centres and thermoluminescence in CaSO4:Dy,Ag phosphor

The defect centres formed in the TL phosphor CaSO4:Dy,Ag are studied using the technique of Electron Spin Resonance. The Ag co-doped phosphor exhibits three glow peaks around 130, 220 and 375 degrees C in contrast with the two glow peaks observed in the CaSO4:Dy phosphor at 130 and 220 degrees C at a gamma ray dose of 1Gy. ESR studies show that the additional peak at 375 degrees C correlates with a Ag2+ centre formed due to gamma irradiation and observable only below -170 degrees C. The Ag2+ centre is characterised by an axial g-tensor with principal values g(parallel) = 2.38 and g(perpendicular) = 2.41. ESR studies further indicate that the precursor to a centre observable at low temperature (-170 degrees C) appears to act as the recombination centre for the TL peak at 375 degrees C; this radical is characterised by the g-values g(parallel) = 2.0023 and g(perpendicular) = 2.0038 and is assigned to SO3- radical. It is observed that there is more incorporation of Ag in the CaSO4:Dy system as compared with that in pure CaSO4 system.     

沉淀法制备CaSO4:Eu和CaSO4:Dy荧光体及发光性能的研究

采用传统的液相沉淀法制备了CaSO4:Eu和CaSO4:Dy粉体,研究并对比了产品的光致发光性能.光谱测试表明,CaSO4:Eu呈近紫外窄带发射.Dy3 掺杂碱土金属硫酸盐因基质不同,发射带有所不同,以CaSO4为基质,Dy3 占据高对称的格位,具有反演对称中心,发射光谱以蓝光发射为主.     

Studies of UV induced phototransferred thermoluminescence in CaSO4:Dy pellets

Single event spectra of a clinical carbon beam have been measured by an ultra-miniature tissue-equivalent proportional counter (UMC). In order to cover the energy range of the Bragg peak, the incident energy of the carbon beam was degraded by aluminium plates. Single event spectra for carbon-events incident to the UMC were analysed and selected at several carbon energies using thin scintillation counters. It was found that the dose weighted lineal energy distributions have a doublet peak structure due to incident carbon beam and fragment contributions.     

Crystal growth and electrical properties of CaSO4:Dy single crystals

Single crystals of CaSO₄:Dy, with and without charge compensator were grown by the solution growth technique. Electrical conductivity was studied at room temperature for diverse concentrations of Dysprosium and showed that it increases upto 0.2 wt % of Dy, beyond which saturation sets in. Electrical conductivity was studied in the region 400 to 700°K and the migration energies estimated for various dopant concentrations. The variation of electrical conductivity and migration energy with diverse dopent concentration is explained on the basis of the theory of defects. The thermoelectric power measurements reveal that the crystals grown are ofP type.