Thermoluminescence Peak In Quartz Research Articles

EPR investigation of the role of germanium centers in the production of the 110°C thermoluminescence peak in quartz

Abstract The identification of the center acting as electron source for the well-known 110 °C thermoluminescence (TL) peak of quartz is of fundamental importance for practical applications in dating and dosimetry. This TL peak was studied in parallel with the electron paramagnetic resonance (EPR) signal of the [GeO 4 ] − center on natural colourless quartz irradiated at room temperature. Immediately after irradiation, the signals of the 110 °C TL peak and of [GeO 4 ] − center decay exponentially in the same way, yielding a lifetime of 50.4 ± 0.9 min at room temperature. Besides, we acquired the isothermal decay curves for the 110 °C TL peak and [GeO 4 ] − center at different temperatures (the samples were held at the selected temperature in the range of 260–308 K). The lifetimes extracted by the isothermal decays were plotted as a function of reciprocal temperature, revealing again the same behavior of the 110 °C TL peak and [GeO 4 ] − center, both characterized by activation energies very close of 0.76 ± 0.07 eV and 0.77 ± 0.07 eV, respectively. All results of the present work clearly show the role of electron source of [GeO 4 ] − center in the emission mechanism of the 110 °C TL peak in quartz.

New numerical model for thermal quenching mechanism in quartz based on two-stage thermal stimulation of thermoluminescence model

The effect of thermal quenching plays an important role in the thermoluminescence (TL) of quartz on which many applications of TL are based. The studies of the stability and kinetics of the 325°C thermoluminescence peak in quartz are described by Wintle (1975), which show the occurrence of thermal quenching, the decrease in luminescence efficiency with rise in temperature. The thermal quenching of thermoluminescence in quartz was studied experimentally by several authors. The simulations work presented in the literature is based on the single-stage thermal stimulation model of thermoluminescence, in spite of that the mechanisms of this effect remain incomplete. This paper presents a new numerical model for thermal quenching in quartz, using the previously published two-stage thermal stimulation of thermoluminescence model.

Thermoluminescence as a probe in bioactivity studies; the case of 58S sol–gel bioactive glass

The formation of a carbonated hydroxyapatite (HCAp) layer on the surface of bioactive materials is the main reaction that takes place upon their immersion in physiological fluids. To date, all techniques used for the identification of this HCAp formation are rather time consuming and not well suited to detailed and rapid monitoring of changes in the bioactivity response of the material. The aim of this work is to explore the possibility of using thermoluminescence (TL) for the discrimination between different bioactive responses in the case of the 58S bioactive glass. Results provided strong indications that the 110 °C TL peak of quartz can be used effectively in the study of the bioactive behaviour of 58S bioactive glass, since it is unambiguously present in all samples and does not require deconvolution analysis. Furthermore, the intensity of the 110 °C TL peak is proven to be very sensitive to the different bioactive responses, identifying the loss of silica which takes place at the first stages of the sequence. The discontinuities of the 110 °C TL peak intensity plot versus immersion time at 8 and 1440 min provide experimental indications regarding the timescale for both the beginning of amorphous CaP formation as well as the end of crystalline hydroxyl-apatite formation respectively, while the spike in the sensitization of the 110 °C TL peak, which was observed for immersion times ranging between 20 and 40 min, could be an experimental feature indicating the beginning of the crystalline HCAp formation.

Potential and limitations of the 210°C TL peak in quartz for retrospective dosimetry

Abstract The potential of the 210 °C Thermoluminescence (TL) peak in quartz for accurate dose reconstruction is studied by comparative TL and optically simulated luminescence (OSL) measurements on quartz extracted from bricks from a mill in a contaminated village of the Techa River valley, Southern Urals, Russia. The cumulative doses measured with TL were found to be continuously lower (on average 10–20%) than the ones measured with OSL for the same sample and using the same luminescence reader. From dose recovery tests, laboratory kinetic analysis and available meteorological parameters of the sample site for the past 100 years, it is concluded that the most likely reason for the discrepancy is thermal fading of the 210 °C TL peak. By applying a suitable model, an effective lifetime of the electron trap of the 210 °C TL peak of 200–700 years is estimated for the moderate continental climate at the sample site. It is concluded that for samples in regions of continental climate and directly exposed to sunlight, dose measurements using the 210 °C TL peak should be restricted to the last 50–60 years. Applications to older samples should only be considered if bricks are not directly exposed to sunlight or if the background dose is small compared to the anthropogenic dose, as the latter will have been acquired during shorter times and will thus not have been subjected to significant thermal fading.

Defect centre responsible for production of 110 ∘ C TL peak in quartz

110 ∘C thermoluminescence (TL) peak in quartz is well known due to its pre-dose effect, which is used in dating technique. The generally accepted mechanism for the production of this peak is based on Ge impurity contained in quartz. Its role is to substitute for Si in SiO 4 tetrahedron and under irradiation gives rise to [GeO 4/e −] − electron centre. Heating for TL read out liberates electron that recombines with hole in [AlO 4/h] ∘ or [H 3O 4/h] ∘ centres emitting photon. The investigation, carried out on blue quartz, green quartz, black quartz, pink quartz, red quartz, sulphurous quartz, milky quartz, alpha quartz and synthetic quartz, has shown that the 110 ∘C TL peak in all these varieties of quartz has no correlation with the respective Ge content. Electron paramagnetic resonance (EPR) measurements on any of these varieties of quartz revealed a signal with g 1=2.0004, g 2=1.9986 and g 3=1.974 and this signal does not appear to correspond to any known EPR signals in alpha quartz. Furthermore, isothermal decay measurements are carried out on the above mentioned EPR signal and 110 ∘C TL peak in alpha, blue and green quartz. A close correlation has been observed in the decay behavior. A new mechanism is proposed based on an interstitial O − centre.

The effects of annealing and irradiation on the sensitivity and superlinearity properties of the [formula omitted] thermoluminescence peak of quartz

Quartz samples which undergo heating and irradiation treatments exhibit changes in their sensitivity to irradiation, as well as in their TL dose response. These changes of thermoluminescence (TL) sensitivity and superlinearity of the 110 ∘ C TL peak of quartz have been the subject of several experimental and theoretical studies, because they form the basis of the predose technique for dating ceramics and for accident dosimetry. In an effort to separate experimentally the effects of irradiation and annealing on the predose effect, three quartz samples of different origin were prepared under three different conditions: unannealed samples, samples annealed at 500 ∘ C , and samples annealed at 900 ∘ C . Complete TL versus dose and sensitivity S versus predose curves were obtained for the dose range of 0.1 < D < 400 Gy . Additional complete sets of data were obtained for samples that underwent a combined predose irradiation and a heat treatment to 500 ∘ C . Although the TL versus dose curves and the sensitivity versus predose data showed very different behaviors, preannealing the samples at 900 ∘ C removed the observed differences that are due to the thermal or irradiation history of the quartz samples. The experimental data is consistent with the assumption that high-temperature anneals and/or high dose irradiation of the samples reduces the concentration of available competitor sites. The concentration of these competitor sites, as described by the Zimmerman model of quartz, is identified as the most important factor in causing the observed differences in predose behavior between quartz samples of different origin. Strong evidence in support of this competitor theory is provided by the estimated equivalent doses (EDs) for the three quartz samples.

Modelling thermal activation characteristics of the sensitization of thermoluminescence in quartz

The sensitization of the ∼110°C thermoluminescence peak in quartz, also termed the ‘pre-dose’ effect, was previously explained using an energy level model including two electron trapping states and two hole centres. The experimental procedure includes a stage of high temperature activation following a relatively large irradiation of the sample. The response to a small test-dose was found to depend on this activation temperature. With different quartz samples, different behaviours of the thermal activation characteristics (TACs) were found. In typical TACs, the sensitivity reached a maximum at ∼500°C, followed by a rather sharp decline in some samples; in others a maximum was reached at ∼350°C followed by a slight decline towards a plateau level. In this work, we show that these behaviours can rather easily be explained within the framework of the two traps–two centres model. This is done by numerical solution of the relevant sets of differential equations governing the different stages of the experimental procedure. The different kinds of dependence were simulated with different sets of trapping parameters. A better insight into the processes taking place is reached, which may have implications in the application of pre-dose dating of archaeological quartz samples and in retrospective dosimetry.

Investigation of the thermal stability of 210°C TL peak of quartz and dating the components of terrazzo from the monastery church of Tegernsee

The lifetime of the thermoluminescence (TL) peak of quartz observed at 210°C using 5°C/s heating rate is assessed using well-dated thermally isolated bricks from a monastery and exposed bricks from warmer climatic zones by comparing the absorbed dose obtained using the 210°C TL peak with those obtained from 310°C TL peak. The lifetimes of the 210°C TL peak calculated for samples collected from thermally isolated excavations and exposed buildings are found to be clusted around 8000–10000 and 600–800 years, respectively. The results proved that 210°C TL peak could be used for dating of samples younger than 1000 years without thermal correction if the samples are thermally isolated from their environment. TL ages are obtained using quartz, polyminerals from brick pieces as well as flint splinters, and other quartz inclusions extracted from the mortar of the terrazzo floor of the monastery church. The measured TL ages and the consistency of the results are discussed. The fine grains in the mortar, which contained calcite/aragonite, could not be dated using thermoluminescence due to presence of a very strong non-radiation induced TL glow.

Luminescence dating of Somero sacristy, SW Finland using the 210°C TL peak of quartz

The 210°C thermoluminescence (TL) peak of quartz, extracted from brick fragments of Somero sacristy (Finland), which were partly elements of construction, were used for the measurement of archaeological dose for the purpose of dating. The annual gamma dose-rate with cosmic component and beta dose rate of bricks were measured using two types of TLD detectors (AL 2O 3–C) inserted in situ and in laboratory, respectively. The improvements in the precision of the TL measurements, components of annual dose assessment are described, and the results of TL age determination are discussed and compared with the archaeologically expected age.

Thermoluminescence dating of terrazzo from the monastery church of Tegernsee (Bavaria, Germany) using the 210 degrees C TL peak of quartz.

Thermoluminescence (TL) is one of the most important physical methods used in archaeometry for dating ceramics. In this study the newly developed procedures based on the use of the 210 degrees C TL peak of quartz were applied to well-dated bricks of the church of the Tegernsee monastery in Bavaria. The resulting TL ages obtained from these well-dated bricks were used as a reference for selection of the suitable measurement procedure and to test the precision of the measurements and the accuracy of the technique. The optimized procedure was applied to the terrazzo fragments from the monastery church. The TL results provide a new understanding of the architectural history of the church. The improved measurement procedure including various dose evaluation techniques and the components of the annual dose assessment are described.

Simulation of the Pre-Dose Effect of the 110(C TL Peak in Quartz

Computer simulations of the pre-dose effect of the 110°C thermoluminescence (TL) peak in quartz are presented, based on an improved trap model. The proposed model includes a deep hole trap acting as reservoir, two recombination centres and two electron traps, of which one is a deep, not thermally disconnected trap. The model and its physical parameters have been chosen to simulate experimental data of pre-dose sensitisation, thermal activation curves and spectral emission. The simulations were performed by numerically solving the corresponding differential rate equations by a standard Runge-Kutta algorithm. It was possible to simulate a whole pre-dose cycle and to explain the shape of the thermal activation curve and linear dose dependencies of the sensitisation for pre-dose and test dose.

On the optical dating signal from quartz

A series of experiments were conducted on the optical dating signal from quartz. Results are presented showing the quantitative equivalence of the light sums of the optically stimulated luminescence (OSL) emitted by quartz under exposure to 514.5 nm light and that of the quartz “325°C“ thermoluminescence (TL) peak. Discrepancies observed between the OSL and TL light sums under “typical” measurement conditions (i.e. when OSL is measured at ∼293 K and the 325°C TL peak is measured at ∼600 K, in both cases observing ultraviolet emissions) are attributed to thermal quenching of luminescence at the recombination centres (non-radiative recombination). The bleach response spectrum (using bleaching wavebands ranging from 400.6 Δ 10.1 nm to 899.1 Δ 13.2 nm) of OSL from quartz (514.5 nm stimulation) was measured and found, within experimental errors, to be indistinguishable from that previously measured for the 325°C TL peak of quartz. Also measured was the thermal dependence of the OSL signal under stimulation by various wavebands ranging from 480.9 Δ 6.8 nm to 861.1 Δ 12.5 nm, in the temperature range from ∼ 100 to ∼ 500 K. Strong thermal assistance was found for all wavebands tested, with the magnitude of thermal assistance increasing as stimulation wavelength increased— behaviour not inconsistent with photoionization. Supplementary work showed that OSL production involves a single-photon-absorption untrapping step. It is concluded that the OSL emitted by quartz under exposure to visible light, and the 325°C TL peak of quartz, originate from one and the same trapped electron population. Furthermore, optical untrapping of this trapped charge population, resulting in both the bleaching of the 325°C TL peak and the prompt emission of OSL, proceeds by the same mechanism: single-photon-absorption photoionization direct to the conduction band.

Thermal Quenching of Thermoluminescence in Quartz

Summary Studies of the stability and kinetics of the 325 °C thermoluminescence peak in quartz are described which show the occurrence of thermal quenching, the decrease in luminescence efficiency with rise in temperature. This phenomenon causes the ‘initial rise’ method of trap depth determination to give spuriously low results which erroneously implies thermal instability of a peak which is suitable for dating. Its presence is confirmed by radioluminescence studies and is shown not to preclude the use of other methods of trap depth determination.