The effect of heat treatment on the thermoluminescence of naturally-occurring calcites and their use as a gamma-ray dosimeter

The feasibility of using naturally-occurring calcite for gamma-ray dosimetry was investigated. Anneal treatment above 350°C increased the sensitivity of all radiation-induced TL peaks except the glow peaks above 300°C. On the other hand, annealing in air, at a temperature of 700°C caused a collapse in the TL sensitivity. The increase in TL efficiency was found to depend on the annealing temperature and time. Heating at 600°C for 5 h and quenching in ambient air are the optimum conditions for TL sensitivity enhancement in the calcite materials investigated. These results are explained using the energy scheme of the pre-dose model of Zimmerman (1971) and in terms of the impurity rearrangements in the crystal lattice induced by heating. It was found that the values of the kinetic parameters E, s and b for TL glow peaks remained unchanged for annealed samples. The TL dose–response curves for stable dosimetric peaks of annealed and unannealed calcite samples could be fitted to the same linear mathematical function. This implies that the annealing process probably does not change the nature of the trapping centers except the low temperature TL peaks at 125 and 160°C of flowstone. The TL dosimetric parameters of calcite samples annealed, including glow curves, fading characteristics, dose–responses, dose-rate responses and energy responses, have also been studied in detail. The response to gamma-rays of annealed calcite samples was found to be linear from 0.05 to 10⁴ Gy. The lower limit of observable doses for each calcite sample was about 0.05 Gy. This offers the possibility of applying the investigated materials for gamma-ray dosimetry within this useful range. These dosimeters can be used in various applications, such as, in industries related to chemical technology (polymerization), food processing and in determining the dose received by the patient during medical examination and treatment.     

Low dose TL characteristics of Nigerian fluorite

Nigerian fluorite has been characterized by β-irradiation for thermoluminescence in the low dose range (40 μGy–72 mGy). The glow curves exhibit 3 peaks recorded at 111 ± 11 °C, 196 ± 2 °C and 282 ± 4 °C at the heating rate of 5 °C s^?1. The two high temperature peaks exhibit a linear response over the range of study. The minimum detectable dose for each of the observed peaks has been determined and the lowest detection limit of fluorite was also determined. A complex fading pattern was observed for the phosphor and the possible source of the TL buildup has been discussed.     

Investigations of thermoluminescence properties of multicrystalline LiF: Mg,Cu, Si phosphor prepared by edge defined film fed growth technique

Thermoluminescence (TL) properties of LiF: Mg, Cu, Si phosphor prepared in multicrystalline form using edge defined film fed growth (EFG) technique has been investigated. The effect of preparation route on TL properties and thermal stability has been studied. To improve the TL dosimetry properties, phosphor is subjected to different annealing temperatures ranging from 250 °C to 450 °C. The shape of the glow curve structure and peak temperature remains similar at different annealing temperatures, however peak intensities vary. The consistency in the glow curve structure with annealing temperature elucidate that TL trapping states are stable in nature. Thermal annealing at 300 °C for 10 min gives maximum TL intensity with main dosimetry peak at 209 °C. The TL intensity of the main dosimetry peak is increased by a factor of five as compared to as-grown crystal. The thermal stability of LiF: Mg, Cu, Si is found to be better than LiF: Mg, Cu, P. Trapping parameters are calculated to have an insight study of defect states. A simple glow curve structure, tissue equivalency, thermal stability, low residual signal, linear response and reusability makes LiF: Mg, Cu, Si a suitable phosphor for radiation therapy, radio diagnostics and personnel dosimetry applications.     

Thermoluminescence,photoluminescence and EPR studies on Mn2+ activated yttrium aluminate (YAlO3) perovskite

Thermoluminescence (TL) measurements were carried out on undoped and Mn²⁺ doped (0.1 mol%) yttrium aluminate (YAlO₃) nanopowders using gamma irradiation in the dose range 1–5 kGy. These phosphors have been prepared at furnace temperatures as low as 400 °C by using the combustion route. Powder X-ray diffraction confirms the orthorhombic phase. SEM micrographs show that the powders are spherical in shape, porous with fused state and the size of the particles appeared to be in the range 50–150 nm. Electron Paramagnetic Resonance (EPR) studies reveal that Mn ions occupy the yttrium site and the valency of manganese remains as Mn²⁺. The photoluminescence spectrum shows a typical orange-to-red emission at 595 nm and suggests that Mn²⁺ ions are in strong crystalline environment. It is observed that TL intensity increases with gamma dose in both undoped and Mn doped samples. Four shouldered TL peaks at 126, 240, 288 and 350 °C along with relatively resolved glow peak at 180 °C were observed in undoped sample. However, the Mn doped samples show a shouldered peak at 115 °C along with two well defined peaks at ～215 and 275 °C. It is observed that TL glow peaks were shifted in Mn doped samples. The kinetic parameters namely activation energy (E), order of kinetics (b), frequency factor (s) of undoped, and Mn doped samples were determined at different gamma doses using the Chens glow peak shape method and the results are discussed in detail.     

Thermally assisted OSL from deep traps in Al2O3:C

The present work suggests an alternative experimental method in order to not only measure the signal of the deep traps in Al₂O₃:C without heating the sample to temperatures greater than 500 °C, but also use this signal for high dose level dosimetry purposes as well. This method consists of photo transfer OSL measurements performed at elevated temperatures using the blue LEDs (470 nm, FWHM 20 nm) housed at commercial Risø TL/OSL systems, after the sample was previously heated up to 500 °C in order to empty its main TL dosimetric trap. The influence of this procedure on specific features such as glow curve shape and sensitivity of the main TL glow peak was also studied.     

Further study on the influence of thermal treatments on the glow curve structure in LiF:Mg,Cu,P (GR-200A)

The influence of various annealing treatments with heating temperatures (T_A) from 240 to 700 °C, with re-annealing at 240 °C, and with a combined re-annealing procedure of 20 min at 270 °C followed by 10 min at 240 °C on LiF:Mg,Cu,P (GR-200A) was investigated. As the T_A increased, the intensity decreased rapidly to almost no signal at 340–380 °C then increased clearly and achieved a maximum at 540 °C. The position of the maximum intensity of the glow curve shifted basically in the direction of higher temperatures with an increase at T_A and achieved a maximum of 279 °C when annealed at 460 °C. The re-annealing influenced both the intensity and the glow curve structure at certain degree. The effect of re-annealing on the glow curve depended markedly on the T_A. With re-annealing at 240 °C, the intensity decreased as T_A increased up to 360 °C then increased and achieved a maximum at 540 °C. The intensity could be restored fully when annealed at above 500 °C, however, the glow curve couldn't be restored fully. With a combined annealing, the shape of glow curve of a sample annealed at above 540 °C or below 320 °C was similar to that of the standard glow curve of LiF:Mg,Cu,P and the intensity and glow curve could be restored completely when annealed in the range 620–660 °C. It seems that the main roles of the re-annealing at 240 °C are to restore partially the intensity of peak 4 and peak shape for LiF:Mg,Cu,P when annealed at above 260 °C, and restore fully the total TL intensity of LiF:Mg,Cu,P when annealed at above 500 °C and the main roles of the combined re-annealing are to reduce the intensity of peak 5 and the total TL intensity, increase the intensity of peak 4 and restore the glow curve shape.     

The analysis of thermoluminescent glow peaks of copper doped ZnS thin films after β-irradiation

In the given study, the thermoluminescence (TL) properties of copper (Cu)-doped ZnS thin films were investigated after β-irradiation at room temperature (RT). It was observed that the glow curve of this material has two broad TL peaks, in which one of them was centered at about 110 °C and the other at about 170 °C for a heating rate of 1 °C s⁻¹ in the temperature range from RT to 350 °C. The additive dose (AD), T_m(E_a)−T_stop, repeated initial rise (RIR), variable heating rate (VHR) and computerized glow curve deconvolution (CGCD) methods were used to analyze its glow curves. These methods indicated that the glow curve of this material is the superposition of a number of first- and general-order glow peaks, or at least due to the distribution of traps. The dose responses and fading process of both peaks were also examined, and it was observed that the dose responses of both peaks have similar pattern. First they follow a good linearity with different slopes and then saturate at approximately same dose level (2 kGy). The low-temperature broad peak nearly disappeared after 1 week storage in the dark at RT. On the other hand, the intensity of the high-temperature broad peak was approximately reduced to 50% of its original value. The TL emission spectrum of this material has two main emission bands, namely, the blue and green bands. The first glow peak emits predominantly in blue region, whereas the second glow peak in the green region.     

Optimization of preparation procedure of LiF:Mg,Cu,Si TLD for improving the reusability

Several thermal treatments in the temperature range from 270 °C to 320 °C (each of 10 min) were tested as a final preparation procedure of LiF:Mg,Cu,Si to improve the protocol of TL readout with less residual signal for the LiF:Mg,Cu,Si TLD. This high sensitivity LiF:Mg,Cu,Si TLD exhibited thermal stability much better than that of the well known LiF:Mg,Cu,P. For LiF:Mg,Cu,Si, a readout temperature up to 300 °C did not affect the TL sensitivity and glow curve structure for 12 cycles of exposure and readout following an initial thermal treatment at 295 °C for 10 min. The residual TL signal also remained negligible.     

Newly developed highly sensitive LiF:Mg,Cu,Si TL discs with good stability to heat treatment

The preparation method and some dosimetric properties of the new LiF:Mg,Cu,Si discs are presented. The effect of heat treatments on LiF:Mg,Cu,Si was investigated. The shape of the glow curve for LiF:Mg,Cu,Si is similar to that for standard LiF:Mg,Cu,P (GR-200A), and shows minimal differences when annealed in the range from 260 °C to 290 °C for 10 min. The TL sensitivity for LiF:Mg,Cu,Si is much lower than that for GR-200A, but is 35 times larger than that for TLD-100 and is slightly higher than that for HMCP. The height of the high-temperature peaks for LiF:Mg,Cu,Si is not only lower than that for GR-200A, but also lower than that for HMCP. The glow curve shape of LiF:Mg,Cu,Si annealed at 260 °C for different times shows minimal differences and TL response remains stable. These results indicate that the new LiF:Mg,Cu,Si disc has a good stability to thermal treatments and a lower residual TL signal.     

Investigation of the optical absorption characteristics of slow-cooled LiF:Mg,Ti (TLD-100)

The optical absorption (OA) spectrum of LiF:Mg,Ti has been studied as a function of dose at two different cooling rates following the 400 °C pre-irradiation anneal in order to further investigate the role of cooling rate in the thermoluminescence (TL) mechanisms of this material. “Slow-cooling” following the pre-irradiation 400 °C anneal substantially decreases the OA bands at 3.25 eV and 4.0 eV, in agreement with the overall loss in TL peaks 2–5 intensity using slow-cooling routines. Slow-cooling appears to shift the maximum intensity of peak 5 to lower temperatures (a behaviour which has been attributed to an enhanced intensity of peak 5a), however, no difference in the shape of the 4.0 eV OA band is detected following “slow-cooling”. Apparently the OA band related to peak 5a is too close in energy to the peak 5 OA band to be observed due to lack of sufficient resolution and spectral deconvolution process or it is not present at room temperature (RT) and formed during heating of the sample. The intensity of the 4.0 eV OA band does not change if the sample (prior to irradiation to a standard dose of 200 Gy) is irradiated to 4 kGy followed by a 500 °C/1 h post-irradiation anneal. This result demonstrates that the loss of intensity at high levels of dose (so-called radiation damage) of TL glow peak 5 results from alteration of the LCs or to the creation of additional competitive centers and is not correlated with the dose behaviour of the TCs.     

A thermoluminescence study of mineral silicates extracted from herbs in the dose range 0.5–5 Gy

The presence of silicates in many personal objects suggests their potential use at low dose as fortuitous dosimeter in an accidental radiological exposure, when conventional dosimetry is not available. The goal of the present work is the dosimetric characterization of mineral silicates extracted from the plant Hibiscus Sabdariffa L, known as Jamaica flower, in the dose range 0.5–5 Gy. By studying the radiation-induced signal in time, the temperature integration region between 210 °C and 250 °C was found to be the most stable and also reduced the effects of thermal fading in the dose reconstruction process; the dose response curve was linear between 0.5 Gy and 5 Gy. By checking the change in sensitivity after repeated exposures to ionizing radiations and to high temperature heating, no variation in the glow curve shape or peak intensities were detected. To eliminate a pre-existing background signal, all the characterization measurements were performed with aliquots “annealed” by a preliminary readout of the TL.     

Study of the thermoluminescence dosimetric properties of window glass

This paper presents the main thermoluminescence (TL) dosimetric characteristics of commercial Turkish transparent window glass. The structure of the glow curves, including the number of peaks, was found to be dose-dependent. A low-temperature glow peak that at 160 °C shifts to higher temperatures was also observed with increasing storage time at room temperature. This result suggests that this TL glow peak is actually made up of two or more overlapping peaks. These we have attributed to the glow peaks at lower temperatures, which decay faster than the ones at higher temperatures with storage time. The thermal fading of the window glass sample at room temperature showed a relatively sharp decay of about 60% occurring over a period of 28 days, after which the decay rate is small for a measured period of 250 days. In order to the improve the post-irradiation stability of the glow curve, the glass samples were heated after irradiation. To remove the unstable TL peaks responsible for the initial rapid fading, post-irradiation heating at 160 °C for 10 min was found to be the most suitable procedure. The dosimetric characteristics of the post-irradiation heated window glass examined in this study include fading, gamma photon dose-response, reproducibility, batch sensitivity, humidity influence, a dose-rate effect and photon energy response. Dose-response was found to be appropriate for dosimetry in the range 5 Gy to 10 kGy. The post-irradiation heating procedure did not affect the main dosimetric characteristics of the window glass samples. The results in this work suggest that the materials could, by using the TL technique, be a suitable candidate for alternative dose measurements in radiation processing, provided that a judicious choice of the post-irradiation heat temperature is made to minimize fading.     

The effect of pre-irradiation annealing on the thermoluminescence of LiF:Mg,Cu, P phosphor grown by EFG technique

LiF crystal doped with magnesium (Mg), copper (Cu) and phosphorous (P) was grown in the form of multicrystalline sheet using Edge-defined film-fed growth (EFG) technique for dosimetry application. These crystals were grown in argon gas atmosphere using graphite crucible and stainless steel die. Dosimetry peak was observed at 210 °C for as-grown crystal. As reported earlier LiF:Mg, Cu, P is a highly sensitive material but losses its sensitivity if annealed at temperature above 240 °C. In this paper, the effect of annealing temperature on thermoluminescence glow-curve structure, maximum peak temperature, peak height and integrated area of the glow peak of EFG grown samples was investigated in detail. Annealing temperature range from 220 °C to 500 °C was considered for the study. Experimental results of the obtained glow curve show that with increase in annealing temperature, glow peak shift towards higher temperature region with substantial increase in TL intensity. Annealing at 500 °C for 10 min gave maximum TL intensity with main dosimetry peak positioned at 233 °C. Change in the defect structure with different pre-annealing temperature was analysed using trapping parameters.     

Thermoluminescence studies of thermally treated CaB4O7:Dy

Borate based thermoluminescence dosimeters (TLD) show high sensitivity and good TL characteristics. One of the promising material amongst the dosimeters is Dy doped CaB₄O₇. Spectrally resolved thermoluminescence of Dy doped CaB₄O₇ shows three glow peaks at about 50 °C, 240 °C and 380 °C, the intensity of the 240 °C glow peak being the maximum. All TL experiments were conducted on a high sensitivity TL spectrometer at Sussex University with a heating rate of 50 °C min^?1. Two main emissions associated with the Dy dopant are observed at ～480 and 580 nm. The samples were subjected to a series of treatments including excitation by X-rays and UV laser radiation. As part of the present research CaB₄O₇:Dy materials were subjected to two different heat treatments; quenching and slow cooling in order to investigate the changes in TL characteristics.     

Thermoluminescence kinetics analysis of α-Al2O3:C at different dose levels and populations of trapping states and a model for its dose response

Kinetic analysis of a α-Al₂O₃ (TLD-500) thermoluminescent (TL) dosimeter was performed following irradiating the samples with ⁶⁰Co gamma rays. The number of glow peaks contained in the complex glow curve of this phosphor was identified using the T_m ? T_stop method, which demonstrates three component glow peaks. A computerized glow curve deconvolution (CGCD) program was used to determine the trapping parameters of the three constituent glow peaks obtained at different dose levels and different populations of trapping states. To analyze the number of constituent glow peaks, we used a kinetic model to describe both the irradiation and heating stages. The predictions of the model for the TL response agreed well with the experimental data when three dosimetry traps were incorporated.     

A comparative study of the thermoluminescence properties of several varieties of Brazilian natural quartz

The following varieties of natural quartz, as the blue, the green, the red, the pink, the black, the sulphurous and the milky quartz, have been investigated concerning their thermoluminescence properties. For comparison sake natural colorless alpha quartz has been include. Since X-rays diffraction analysis has shown that all of them have the same crystal structure as the alpha quartz, it is expected that no great change in the TL property should be found, however, that was not the case. The TL peaks at 110, 175, 220, 325 and 375 °C observed in the alpha quartz are not found in all the varieties of quartz, for instance, the sulphurous quartz presented only 110° and 245° peaks, the pink one presented just 110, 220 and 375 °C peaks and so on. In respect to TL response as function of gamma ray dose a quite varied behavior has been observed and discussed.     

Thermoluminescence characteristics of hydrogenated amorphous zirconia

This paper reports the experimental results concerning the thermoluminescent (TL) characteristics of hydrogenated amorphous zirconium oxide (a-Zr:H) powder prepared by the sol–gel method. The advantages of this method are the homogeneity and the purity of the gels associated with a relatively low sintering temperature. Hydrogenated amorphous powder was characterized by thermal analysis and X-ray diffraction. The main TL characteristics investigated were the TL response as a function of the absorbed dose, the reproducibility of the TL readings and the fading. The undoped a-Zr:H powder presents a TL glow curve with two peaks centered at 150 and 260 °C, respectively, after beta irradiation. The TL response a-Zr:H as a function of the absorbed dose showed a linear behavior over a wide range. The results presented open the possibility to use this material as a good TL dosimeter.     

Thermoluminescence and optically stimulated luminescence characteristics of Al2O3 doped with Tb

In the present work policrystals of α − Al₂O₃ doped with terbium were synthesized using the solvent evaporation method. The samples were prepared using Al(NO₃)₃·9H₂O and Tb(NO₃)₃·5H₂O reagents, with Tb concentrations between 1 and 5 mol% and thermally treated at high temperature above ∼1400 °C. X-ray diffraction measurements showed the α-phase formation of samples. TL glow curve presented an intense peak at ∼190 °C and two other with low intensity at 290 and 350 °C after gamma irradiation. The best doping concentration which presented high luminescence was the sample doped with 3 mol% of Tb. TL spectra and fluorescence measurements showed similar luminescence spectra with lines attribute to Tb³⁺ ions. A linear behavior to gamma dose between 1 and 20 Gy was observed in TL, using 190 °C peak as well as in OSL signal, this last carried out using 532 nm wavelength stimulation.     

The effects of thermal treatments on the thermoluminescence properties of biogenic minerals present in the seashells

In this study, thermoluminescence (TL) properties of the biogenic minerals present in the seashell samples at different temperatures and annealing times have been studied. Three explicit peaks are seen in the glow curves roughly at 100°C, 180°C, and 380°C. One of the prominent results is that annealing above 600°C affects enormously the TL intensity, whereas no remarkable TL intensity is observed for unannealed samples. The highest intensity and area under the curve were observed at 700°C annealing temperature, and 180 minutes annealing time and 1500 times bigger than the unannealed samples. A linear dose response is observed between 2.4 and 72?Gy and beyond this value, a sublinear relation is observed. Unfortunately, a huge decrease in TL intensity is observed about 51% of its initial value, after 5 hours of storage time.