Study of the 110°C TL peak sensitivity in optical dating of quartz

As the 110°C TL emission in quartz uses the same luminescence centers as the OSL emission, the 110°C TL signal from a test dose may be used to monitor the OSL sensitivity change. It is thus important to study the relationship between the 110°C TL peak and the OSL sensitivity in studies related to optical dating from quartz. We have conducted a series of experiments using sedimentary quartz, where the annealing temperatures were varied between 260 and 1000°C before the measurement of OSL and 110°C TL sensitivities. Another series of experiments on two sedimentary quartz samples investigated the 110°C TL peak and OSL dose-dependent sensitivity change after different annealing temperatures. In these experiments, the 110°C TL and OSL signals from the test dose are shown to have similar sensitization characteristics: the 110°C TL sensitivity change is proportional to the OSL sensitivity change if the annealing temperature is lower than 500°C. It is concluded that the 110°C TL signal can be used to correct the OSL sensitivity change in the single-aliquot additive-dose protocol.     

Lifetime estimation of thermoluminescence traps in granitic quartz

Abstract

Thermoluminescence (TL) traps in granitic quartz are potential geochronometers for ages of up to billions years. TL sensitivity is believed to be a measure of the population of TL traps. Their lifetimes can be roughly estimated either by isothermal annealing or by an empirical approach. The former is applicable to radiation sensitive traps corresponding to > 200°C TL when first order kinetics is assumed. The lifetimes are found to be several orders longer than those of trapped electrons. The lifetimes of thermally sensitive traps (< 200°C TL) are estimated from empirical curves that are constructed from data from granitic quartz of known age. It is found that the lifetime increases with the trap depth.     

Luminescence sensitivity changes of quartz by bleaching,annealing and UV exposure

The sensitivities of quartz luminescence signals to dose were studied after ionizing irradiation, ultraviolet (UV) exposure and different annealing conditions. The relationship between the 110 v °C thermoluminescence (TL) and optically stimulated luminescence (OSL) were studied on the same aliquot by looking at the ratio of both signals created by a test dose. It is suggested that the sensitivity changes of both signals are closely related, but not identical. Significant differences are observed when annealing to temperatures higher than 500 v °C. A modified model was proposed to interpret the observations. The similarity is interpreted as the same R hole centers are shared by both signals, whereas 110 v °C TL only uses additional R hole centers. Dramatic changes in luminescence sensitivity for quartz relate to the phase changes.     

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.     

Effect of annealing and fuel type on the thermoluminescent properties of Li2B4O7 synthesized by Solution Combustion Synthesis

The objective of this work is to investigate the effect of annealing and fuel type on the thermoluminescent (TL) properties of Li₂B₄O₇ (LBO) synthesized by Solution Combustion Synthesis. In this study, LBO:Cu,Ag was synthesized using four fuel combinations of urea, a urea/ammonium nitrate mixture, glycine, and a glycine/ammonium nitrate mixture. Annealing was performed at temperatures from 800 °C to 900 °C for periods from 20 min to 120 min. The samples were then studied by X-ray diffraction (XRD) and TL. The results show that, among the parameters investigated, the annealing temperature and duration are the main parameters affecting the TL sensitivity (up to a factor of 2), which may be correlated with crystallite sizes. We also observed some effect of annealing on light sensitivity, but the effect was at most a reduction from a TL loss of ∼20% to ∼2% for 3 h exposure to room light. The main conclusion is that Solution Combustion Synthesis is an appropriate method to obtain LBO:Cu,Ag suitable for temperature sensing applications, the post-synthesis annealing regime being one of the parameters that can affect the signal intensity and, to a lesser extent, the light sensitivity.     

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.     

Synthesis and thermoluminescence characterization of MgB4O7:Gd,Li

Magnesium tetraborate (MTB) doped with rare earth elements were synthesized by solid state sintering technique. Among the different rare earth dopants studied in this phosphor, gadolinium doped phosphors resulted in a single intense dosimetric peak at 250 °C and this is the first report in rare earth-doped MgB₄O₇ with a glow peak above 200 °C Photoluminescence (PL) and thermoluminescence (TL) studies were performed with this phosphor after exposing the powder samples to ionizing radiation. Monovalent dopants, including Na, Li and Ag, were found to increase the TL sensitivity of the MgB₄O₇:Gd phosphor without a shift in the TL peak temperature. The TL emission spectra showed characteristic emission of the host lattice, which showed an increase on doping with rare earth or monovalent codopants. The TL sensitivity, dose response curve, and post-irradiation storage stability were studied for the possible use of this material in radiation dosimetry applications. The TL parameters, such as the activation energy, the frequency factor, and the order of kinetics were determined for the Gd-doped MgB₄O₇ phosphor. The phosphor was found to be reusable after a few cycles of irradiation and annealing. The post-irradiation storage stability studies showed that this near tissue-equivalent phosphor, which has a gamma sensitivity five times that of TLD-100, is suitable for medical dosimetry applications.     

Red thermoluminescence (RTL) sensitivity change in quartz

This study investigated changes in the thermoluminescence sensitivity of volcanic and plutonic quartz following irradiation and annealing treatments with the aim of improving the accuracy of red thermoluminescence (RTL) dating. The response to X-ray irradiation (49 Gy) and RTL readout to 450 °C at a rate of 1 °C s^?1 was repeated 12 times and the sensitivity change induced by doses ranging from 49 to 293 Gy was examined. The results of these two experiments revealed that the final enhanced ratio of the sensitivity of plutonic quartz is 2.1–2.8 and 2.2–2.3 for two types of analyzed samples, much greater than that of volcanic quartz. To examine the thermal stability of quartz, several annealing treatments were performed from 300 to 900 °C for 100 min. An annealing treatment of 500 °C for 100 min resulted in a strong enhancement of RTL emission intensity for plutonic quartz, approaching the level for volcanic quartz. Finally, the single aliquot regeneration (SAR) method was applied to evaluate the absorbed dose, D_e, for aliquots irradiated with a known-dose ranging from 195 to 1952 Gy. All SAR D_e values obtained with volcanic quartz were in good agreement with the known dose values; whereas for plutonic quartz large uncertainties in D_e were obtained due to a marked sensitivity change. The magnitude of the RTL sensitivity change of quartz depends on dose and annealing treatment, and is clearly dependent on a classification of quartz based on thermal history.     

A comparative study of the luminescence characteristics of polymineral fine grains and coarse-grained K- and Na-rich feldspars

The IRSL and post-IR IRSL (pIRIR) signal characteristics of polymineral fine grains are investigated and compared with those of K- and Na-rich feldspar extracts. TL signal loss after IR and pIRIR stimulations occurs mainly at around 320 °C for polymineral and Na-feldspar samples and around 410 °C for K-feldspar samples, when a preheat temperature of 250 °C for 60 s is used. After preheating to a higher temperature (320 °C for 60 s) all samples show a TL reduction around 410 °C in the blue detection window. Pulse annealing experiments for IRSL and pIRIR signals for preheats between 320 °C and 500 °C indicate that the signal stabilities are similar among the different feldspar types, when a higher preheat temperature (>320 °C) is used. Thermal activation energies for IRSL and pIRIR signals are largest in K-feldspar and smallest in polymineral fine grains, in both blue and UV detection windows for both fast time-resolved (TR) and continuous wave (CW) signals. These results suggest that IRSL and pIRIR signals in polymineral fine grains originate mainly from Na-feldspar grains; these signals are less thermally stable than those from K-feldspar, but a more stable signal (presumably from K-feldspar grains) can be obtained using a higher preheat temperature.     

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.     

Post-IR IRSL production in perthitic feldspar

A museum sample of perthitic feldspar was used to study the production of post-IR IRSL signals. It was found that traps responsible for low temperature (∼230 °C) TL peaks play an unexpectedly important role in post-IR IRSL production. During the production of the IRSL signal during low temperature IR stimulation (100 °C), electrons are optically transferred from IRSL traps into these TL traps which have been emptied by the preceding preheat at 320 °C. Subsequent heating to 300 °C causes thermal transfer of these electrons from these traps back into previously emptied IRSL traps which are related to the high temperature TL peaks. IR stimulation of these electrons results in post-IR IRSL. Thus the initial source of the post-IR IRSL signal is the same as the IRSL signal, with a role being played by intermediate traps that give rise to TL signals between 200 and 250 °C, and the final source is similar to that of the IRSL signal. Therefore the post-IR IRSL signal is a by-product of the production of the IRSL signal. It was also found that post-IR IRSL production with high post-IR IR stimulation temperatures (e.g. >230 °C) additionally includes a small contribution from the post-IR isothermal decay of high temperature TL peaks that are not sensitive to IR stimulation at low stimulation temperatures.     

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.     

Gamma ray induced sensitization of 110°C TL peak in quartz separated from sand

We have investigated the gamma ray induced sensitization of the 110°C TL peak in quartz, separated from sand, in the dose range 30–750 Gy. A pre-dose of 100 Gy followed by annealing at 500°C for 1 h yielded an optimum sensitization factor of 14.2 for a test gamma dose of 0.5 Gy; this factor decreases slowly up to the studied pre-gamma dose of 750 Gy. From ESR studies carried out in the temperature range 25–550°C, the formation of E′₁-centres and their subsequent decay (at temperatures >400°C) have been observed. The released charge carriers (electrons) may lead to elimination of competitors (as a result of their filling up). Thus, the radiation-induced sensitization of the 110°C TL peak could be due to elimination of the competing deep traps.     

Optically stimulated luminescence from CaSO4:Eu – Preliminary results

A new OSL phosphor CaSO₄:Eu was developed. The phosphor shows good OSL sensitivity which is about 55% of commercially available Al₂O₃:C. The phosphor also shows good TL sensitivity and the dosimetric peak, which appears around 186 °C, has sensitivity nearly 50% of Al₂O₃:C. After OSL readout of the irradiated sample, the TL peak around 250 °C depletes completely, with partial depletion of peak around 186 °C. Since the traps responsible for the high temperature peak are involved for the observed OSL, the sample shows low post-irradiation fading. The OSL decay is similar to Al₂O₃:C. Thus this phosphor due to its good OSL sensitivity, linear dose response, low fading and simple preparation technique could be useful for radiation dosimetry applications.     

Luminescence lifetimes in quartz: dependence on annealing temperature prior to beta irradiation

It is well known that the thermal history of a quartz sample influences the optically stimulated luminescence sensitivity of the quartz. It is found that the optically stimulated luminescence lifetime, determined from time resolved spectra obtained with pulsed stimulation, also depends on past thermal treatment. For samples at 20°C during stimulation, the lifetime depends on beta dose and on duration of preheating at 220°C prior to stimulation for quartz annealed at 600°C and above, but is independent of these factors for quartz annealed at 500°C and below. For stimulation at higher temperatures, the lifetime becomes shorter if the sample is held at temperatures above 125°C during stimulation, in a manner consistent with thermal quenching. A single exponential decay is all that is required to fit the time resolved spectra for un-annealed quartz regardless of the temperature during stimulation (20–175°C), or to fit the time resolved spectra from all samples held at 20°C during stimulation, regardless of annealing temperature (20–1000°C). An additional shorter lifetime is found for some combinations of annealing temperature and temperature during stimulation. The results are discussed in terms of a model previously used to explain thermal sensitisation. The luminescence lifetime data are best explained by the presence of two principal luminescence centres, their relative importance depending on the annealing temperature, with a third centre involved for limited combinations of annealing temperature and temperature during stimulation.     

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.     

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.     

Thermoluminescent dosimetric characteristics of annealed quartz

In the given present study, the effect of pre-irradiation heat treatment at 500 and 600 ^°C on the glow peaks of synthetic quartz was examined as a function of annealing time to obtain an optimum annealing procedure. It was observed that the annealing time is not a strongly sensitive parameter to change the intensities of glow peaks. On the other hand, the intensities of glow peaks between room temperature (RT) and 200 ^°C were continuously increased during successive readings after heat treatments. Moreover, the intensities of glow peaks above 250 ^°C have good stabilities. The obtained repeatability of a glow peak at ～320 ^°C over 10 cycles is within 5% after the application of annealing at 600 ^°C for 1 h. The general thermoluminescent dosimetric characteristics of synthetic quartz, such as the dose–response, signal fading as a function of storage time, and reusability were also tested using the annealing condition at 600 ^°C for 1 h. It was observed that dose-response behaviours of all glow peaks are similar to each other. They first follow linear part and then saturated at different dose levels. Peak 1 completely disappeared after 1 month storage in the dark room at RT. On the other hand, the intensity of peaks 2+3 was approximately reduced to 15% of its original value whereas the other peaks (P4–P5) were not sufficiently affected during this period.     

Luminescence from NaCl for application to retrospective dosimetry

The alkali halide NaCl (Common salt) is an environmentally-abundant phosphor of considerable potential for retrospective dosimetry and radiological event analysis due to its high sensitivity to ionising radiation when analysed by Thermoluminescence (TL), Optically-stimulated luminescence (OSL) or Infrared-stimulated luminescence (IRSL). We report here aspects of luminescence from NaCl relevant to the development of valid protocols for measurement of recent ionising radiation exposure. The timescale of interest in this application is from days to decades, hence our emphasis is on detection and characterisation of TL emission in the 100–300 °C range, and of OSL and IRSL emissions measured following only low temperature preheating (160 °C). A collection of 19 salt samples was assembled, including samples of rock salt and domestic salt produced by evaporation from brine. Analysis of TL emission spectral changes, together with previously reported TL, OSL and IRSL sensitivity changes, confirmed activation of sensitivity change by exposure to temperatures exceeding 160 °C. Kinetic analysis using Chen's method found E = 0.943 eV and s = 5.1 × 10¹¹ s^?1 for the 100 °C TL peak, giving a lifetime at 20 °C consistent with previous calculations and in the range of 7–14 h.     

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.