T.M. Piters

Limitation of peak fitting and peak shape methods for determination of activation energy of thermoluminescence glow peaks

This paper shows the limitation of general order peak fitting and peak shape methods for determining the activation energy of the thermoluminescence glow peaks in the cases in which retrapping probability is much higher than the recombination probability and the traps are filled up to near saturation level. Right values can be obtained when the trap occupancy is reduced by using small doses or by post-irradiation partial bleaching. This limitation in the application of these methods has not been indicated earlier. In view of the unknown nature of kinetics in the experimental samples, it is recommended that these methods of activation energy determination should be applied only at doses well below the saturation dose.

Thermally and optically stimulated luminescence correlated processes in X-ray irradiated KCl: Eu2+

Abstract The effect of optical bleaching on thermoluminescence (TL) and thermal bleaching on optically stimulated luminescence (OSL) outputs in X-ray irradiated KCl : Eu 2+ have been investigated. The X-ray induced glow curves reveal three main peaks located at 370, 410 and 470 K . Illumination with 560 nm light leads to a drastic change of the TL glow curve. The 470 K peak is destroyed during bleaching. The other peaks initially increase in intensity and only after sufficiently long bleaching begin to decrease. After long-time bleaching, the TL peaks in X-ray irradiated crystals look like the TL peaks found in UV irradiated crystals. The effect of thermal bleaching on OSL is also very pronounced. The temperature dependencies show a step-by-step decrease of the OSL intensity correlated with the positions of the TL peaks. The result obtained shows that centers responsible for the TL peaks participate in OSL, but this participation seems not to be direct and is complicated by processes accompanying the F center bleaching.

Thermoluminescence, Optical Stimulated Luminescence and Defect Creation in Europium Doped KCl and KBr Crystals

Europium doped alkali halide single crystals have been the subject of very intensive investigation due to its applications in digital medical radiography, optical memories and environmental dosimetry. The performance of these phosphorous materials exhibited in both thermoluminescence and optical stimulated luminescene, is generally explained through mechanisms where the photoionization of impurity is involved. However, no evidence of the presence of the Eu3+ ion has been reported yet. In this paper we present experimental insight into the defect creation processes generated by ionizing radiation, as well as ultraviolet light with energies below the band gap in both phenomena, which show the same 420 nm emission. The F and Fz centers are clearly related to the thermoluminescence glow curve. The results show a similar thermoluminescence and optical stimulated luminescence origin and may suggest the existence of a non-excitonic mechanism involved in the defect creation with ultraviolet non-ionizing radiation light.

β-ray irradiation thermoluminescence and dosimetric characterization of KCl1−xBrx:Eu2+ mixed crystals

Abstract Thermoluminescence and dosimetric characterization of KCl 1− x Br x :Eu 2+ mixed crystals exposed to β -ray irradiation have been studied as a function of composition x in the mixed solid solution. Significant changes on its thermoluminescence properties and dosimetric behavior have been found concerning pure end KCl:Eu 2+ and KBr:Eu 2+ components. The results indicate a minimum thermoluminescence efficiency at about middle composition. The addition of small amount (1.0%) of Br − ion to KCl is more effective in producing a higher thermoluminescence efficiency and lower fading. It also enhances the linear response as a function of irradiation dose increasing greatly its application as an ionizing thermoluminescence dosimeter.

UV induced afterglow of KCl:Eu,KBr:Eu and NaCl:Eu at low temperature

Abstract We propose a model for the production of defects by non-ionising radiation in impurity-doped alkali halides based on the formation of impurity-trapped excitons by excitation of the impurity, instead of ionisation of the impurity as has been proposed before. The dissociation of the trapped excitons into FZ and H centres in our model is similar to the case of the formation of F and H centres induced by ionising radiation in pure alkali halides. To gather information about the mechanism of defect creation by non-ionising radiation, we investigate the afterglow (AG) emission induced by UV light at low temperature (20 K ) in three different alkali halides: KCl, KBr and NaCl doped with Eu impurity. We conclude that the AG emission can be split into two components; one of them has a fast decay and the other one remains for several minutes, decaying according to t−1/2. This second component has a close relation with the thermoluminescence emission. We show that the decay of the second component can be explained within the framework of our model if we assume that the H centres migrate along lines. We suggest that these lines are dislocation lines.

Dose response of thermoluminescence emission spectra of LiF:Mg,Ti with different Mg, Ti impurity concentrations

Abstract The dose response of the TL emission spectra of an LiF:Mg,Ti (TLD-100) sample and three LiF:Mg,Ti samples with different impurity concentrations (0–6 ppm Ti and 80–100 ppm Mg) have been measured. At a dose less than 22 Gy the emission spectrum of the TLD-100 sample comprises one emission band at 420 nm. The sample without Ti shows also one emission band but now at 620 nm. The spectra of the other two samples comprises two emission bands at 420 nm and 620 nm of which the intensity of the 420 nm band increases with increasing Ti concentration. The dose response of the glow peaks is different for peaks at different temperatures and emission bands. From these observations it can be concluded than in LiF:Mg,Ti at least some of the traps and luminescent centers are coupled.

On the role of dislocations and aggregates in UV induced afterglow luminescence of KCl:Eu at low temperatures

Afterglow (AG), thermoluminescence (TL) and photoluminescence efficiencies in KCl:Eu were investigated in samples annealed at 773 K with high Eu–vc dipole concentration, samples aged at 373 K with high aggregate concentration and plastically deformed samples enriched with dislocations. AG and TL efficiencies increase significantly for samples with high concentration of aggregates. Plastically deformed samples show a greater efficiency of AG and TL compared to undeformed samples. However, the formation of aggregates during the ageing procedure is strongly reduced in deformed samples. Furthermore, the low temperature peaks in the TL glow curve are absent in deformed and aged samples. We interpret these results as evidence for the participation of dislocations in the AG process and ascribe the relatively high AG efficiency of aggregates to a preferential formation of aggregates along dislocations.