Synthesis, characterization and thermoluminescence of MgO:Li,Tb,Sm phosphor for high dose gamma dosimetry applications

A detailed TL investigation on MgO:Li,Tb,Sm phosphor has been carried out by studying several TL characteristics - TL glow curve structure, dose response, linearity dose behaviour, fading and reproducibility. TL glow curve structure of the phosphor reveals the presence of two TL glow peaks. The main TL glow peak of high intensity is observed at high temperature side i.e. at 162 °C and another peak of low intensity is observed at 316 °C. Further, the effect of dose on TL response of the phosphor has been studied and a new behaviour is noticed. With increasing doses, the position of main TL glow peak is similar while the second TL glow peak vanishes at higher doses. A linear TL response is observed from 10 Gy-700 Gy and becomes sublinear above 700 Gy. Low TL fading characteristics and good reproducibility have also been observed. Encouraging results suggest the applicability of doped MgO phosphor for the detection of gamma rays.

Phototransferred thermoluminescence characteristics of microcline (KAlSi3O8) under 470 nm blue- and 870 nm infrared-light illumination

We report phototransferred thermoluminescence (PTTL) induced in microcline by 470 nm blue- and 870 nm infrared-light. A conventional thermoluminescence (TL) glow curve measured from a sample irradiated to 40 Gy produces five composite TL glow peaks P1, P2, P3, P4 and P5 at 90, 123, 166, 298 and 391 °C respectively. The sample produces PTTL peaks also identified as P1, P2, P3 and P4 following illumination by blue or infrared light after irradiation to 40 Gy and preheating to 400 °C. Step-annealing suggests the presence of deep electron traps associated with a signal beyond 500 °C. However, preheating to 500 °C and exposure to blue or infrared light does not produce significant PTTL peaks. For doses between 40 Gy and 100 Gy, the maximum PTTL is emitted within 60 and 150 s of blue light illumination. On the other hand, the same feature under the infrared light illumination occurs within 100-200 s of illumination. PTTL peaks P1, P2, P3 and P4 reproduced under blue light illumination have a linear dose response between 10 Gy and 100 Gy and those reproduced under infrared light illumination have a superlinear dose response between 10 and 100 Gy. In contrast, donor peak P5 in both cases follows sublinear dose response within the same dose range. Fading of PTTL peaks P1, P2, P3 and P4 as well as the donor peak P5 are negligibly small under blue light illumination compared to that of infrared light illumination. PTTL glow curves are also found to be properly reproducible.

Stimulated luminescence; Analysis of complex signals and fitting of dose response curves using analytical expressions based on the Lambert W function implemented in a commercial spreadsheet

Thermoluminescence (TL) and optically stimulated luminescence (CW-OSL, LM-OSL) are widely used by the scientific community in different applications. In order for the information of a glow or decay curve to be used correctly, the deconvolution of the corresponding curve is essential. Nowadays, there are plethora of deconvolution methods with none of them being dominant and universal. Recently, researchers created some new analytical equations for the TL, CW-OSL and the LM-OSL phenomena, based on the Lambert W function, with the use of a single master equation, as well as some new dose response curves based on a) the simple One Trap One Recombination (OTOR) model and b) the more complex Two Traps One Recombination (TTOR) model. The main aim of the study is to recreate these five expressions in different Excel spreadsheets, for a more practical use. The first step is the creation of a computational code of the Lambert W function in VBA at Excel. After that aim is achieved, five spreadsheets were created, namely the TL deconvolution, the CW-OSL deconvolution, the LM-OSL deconvolution, the OTOR model Dose response and the TTOR Dose response. In order to run some tests using these spreadsheets, four different sets of experimental data originated from different sources were used each time, with the calculated values being compared to the literature. In the end, the present study provides some notes and discussion about the applications of the newly created deconvolution spreadsheets.

CONDUCTION BAND-VALENCE BAND THEORY OF TL AND OSL: EMPHASIS ON DELOCALIZED TRANSITIONS AND EXPLANATION ON SOME UNUSUAL EFFECTS

We discuss some unusual thermoluminescence (TL) and optically stimulated luminescence effects. We focus on luminescence due to transitions of electrons or holes through the conduction or valence band, respectively. We deal with non-linear dose dependence and non-monotonic dose dependence and also dose-rate effects sometimes reported. Also, is discussed the sensitisation of a sample due to the combined effect of irradiation and annealing, occurring in quartz samples and other materials. Another effect presented is the occurrence of anomalously high activation energies and frequency factors and its possible theoretical interpretation. Also, are considered the effects of anomalous fading and anomalous stability. Yet another phenomenon is concentration quenching. Here, the intensity of emitted TL depends non-monotonically on the concentration of the impurity responsible for the emission. The explanations given to these phenomena are based on the numerical solutions of the relevant sets of differential equations as well as approximate analytical treatment.

Thermoluminescence analysis of co-doped NaCl at low temperature irradiations

The thermoluminescent response and kinetics parameters of NaCl, doubly activated by Ca-Mn and Cd-Mn ions, exposed to gamma radiation are analyzed. The doped NaCl samples were irradiated at relative low temperature, i.e. at the liquid nitrogen temperature (LNT) and at dry ice temperature (DIT), and the glow curves obtained after 2 Gy of gamma irradiation were analyzed using the computerized glow curve deconvolution (CGCD). An evident variation in the glow curve structure after LNT and DIT was observed. It seems that different kinds of trapping levels are activated at relative low temperature. The original two prominent peaks in compositions A (Ca,Mn) and B (Ca,Mn) have been changed in only one main peak with satellites in the low temperature side of the glow curves. In compositions C (Cd,Mn) and D (Cd,Mn), low temperature peaks become stronger and prominent than the high temperature peaks; this effect could be explained considering that the trapping probability for low temperature traps, the one very close to the conduction band, is enhanced by low temperatures during irradiation.

Non-monotonic dose dependence of thermoluminescence

The thermoluminescence (TL) intensity in different materials is usually a monotonic increasing function of the dose, which quite often reaches a saturation value. In several materials, however, non-monotonic dose dependence has been observed. The TL intensity reached a maximum at a certain dose and decreased at higher ones. Some authors refer to this effect as 'radiation damage'. In the present work, we show that the non-monotonic dependence can easily be demonstrated to result from competition between transitions model with two trapping states and two kinds of recombination centres. Two kinds of competition are considered. One in which competition during excitation dominates, the filling of the active luminescence centre is non-monotonic, and the resulting TL is non-monotonic. In the other, the filling of traps and centres is monotonically increasing, but the competition during heating causes TL intensity to reach a maximum and decline at higher doses.

Thermoluminescence of terbium sensitised by samarium in CaF2

Thermoluminescence (TL) in sintered CaF2 doped with Tb4O7 has been studied for UV and X-ray irradiation. Three TL glow peaks for the Tb4O7 doped sample appeared in the temperature regions of about (1) 347-353 K, (2) 378-383 K and (3) 453-458 K, when heated at a rate of 20 K min(-1) after UV or X-ray irradiation at room temperature. It has been found that the 378 K peak intensity of the samples co-doped with Tb4O7 and Sm2O3 became stronger when compared with those doped with only terbium or samarium ions, and the TL peaks of (1) 347-353 K and (3) 453-458 K were not observed. The intensity of the 378 K peak of the co-doped sample was 12.9 times that of the sample doped only with Tb4O7. From the TL spectra and the excitation and emission spectra of photoluminescence for the CaF2 doped activators, it is concluded that the TL of Tb3+ ions is sensitised by the existence of Sm3+ ions. The 378 K TL peak may also be suitable for UV radiation dosimetry.