TL Peak Research Articles

Thermoluminescence and optically stimulated luminescence of gamma‐irradiated mineral zircon

AbstractThermoluminescence (TL) manifested by gamma‐irradiated mineral zircon has shown a strong TL peak at about 165 °C which is due to recombination of electrons and Dy3+ related shallow hole traps. After they have been removed by a short preheat we have observed two TL peaks at 300‐320 °C and ≈420 °C, which are mainly due to recombination of electrons and Tb3+ related hole traps centres yielding its characteristic luminescence. The experimental results indicate that optically stimulated luminescence (OSL) is due to luminescent emission of Tb3+ ions and [SiO4]4– groups. The deep traps related to the 420 °C TL peak contribute to the Tb3+ related OSL. The deep traps related to the 300‐320 °C TL peak contribute to OSL associated with the luminescent emission of [SiO4]4– groups. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

High temperature thermoluminescence of BaFCl:Eu2+ X‐ray storage phosphor

AbstractThermoluminescence (TL) of Eu2+‐doped BaFCl polycrystalline powders X‐ray irradiated at room temperature show several TL peaks at 364 K, 408 K, 470 K, 524 K and 646 K. Thermally activated recombination processes responsible for TL have been studied using complementary techniques as TL and its bleaching, diffuse reflectance, X‐ray excited luminescence (XL) and photostimulated luminescence (PSL). Experimental results indicate that F(Cl–) centres are the dominant electron trap centres, the Eu2+‐trapped hole aggregate centres playing the role of recombination centres. The 470 K and 646 K TSL glow peaks are assigned to the recombination inside the triple aggregates (Eu2+ ‐ hole centre ‐ F(Cl–) centre). The remaining 408 K and 524 K TL peaks are tentatively assigned to recombination between F centres and double aggregates (Eu2+ ‐ hole centre). (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Dosimetric characterization of wollastonite‐teflon composites

AbstractIn this work, the thermoluminescent properties of pellets containing powdered Wollastonite embedded in Teflon were studied. The preliminary results using gamma rays from a 60Co source showed linearity at the calibration curve between 0.5 Gy and 10 Gy. The main TL peaks are located at 125, 200 and 245 °C. The repeatibility of TL response presented a maximum coefficient of variation of 6.3%. The material can be used in successive irradiation‐reading‐annealing cycles without an appreciable change in its sensitivity. The calibration curve for a gamma source (60Co) up to 20 kGy and the minimum detection limits were obtained. The results show that these Wollastonite‐Teflon pellets present possibilities for use as TL dosimeters. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Comparative study of thermoluminescent responses of diverse CVD diamonds

The thermoluminescent properties of two types of transparent polycrystalline chemical vapour deposition (CVD) diamonds, and of a non-transparent freestanding CVD cutting material, type CVDITE-CDM, were investigated to be used as detectors of X-rays. The reproducibility in TL response of both types of diamonds was measured with the use of radiation emitted from the 55Fe and 137Cs radioisotopes. A significant change of TL sensitivity after the repeated irradiation/readout cycles and of annealing procedures of the transparent CVD diamonds was observed. In contrast to it, the CVDITE-CDM samples containing a non-diamond component show reproducible TL properties. The sublinear TL response of CVDITE-CDM diamonds for doses higher than 1.5 Gy is presented. It is demonstrated that the influence of daylight on their TL response sensitivity can be eliminated by preheating at 250 °C for 30 s. The Raman and photoluminescence spectra of the samples at room temperature are analyzed. The content of the non-diamond component in different CVD diamond samples estimated by these methods is correlated to the relevance of a TL peak at a temperature of ≈ 310 °C.

Correlated ESR, PL and TL studies on Sr 5(PO 4) 3Cl:Eu thermoluminescence dosimetry phosphor

Electron spin resonance (ESR), thermoluminescence and photoluminescence studies in Eu 2+ activated Sr 5(PO 4) 3Cl phosphor are reported in this paper. The Sr 5(PO 4) 3Cl:Eu 2+ phosphor is twice as sensitive as the conventional CaSO 4:Dy phosphor used in thermoluminescence dosimetry of ionizing radiations. It has a linear response, simple glow curve, emission peaking at 456 nm. The defect centers formed in the Sr 5(PO 4) 3Cl:Eu 2+phosphor are studied by using the technique of ESR. A dominant TL glow peak at 430 K with a smaller shoulder at 410 K is observed in the phosphor. ESR studies indicate the presence at three centers at room temperature. Step annealing measurements show a connection between one of the centers and the dominant glow peak at 430 K. The 430 K TL peak is well correlated with center I, which is tentatively identified as (PO 4) 2− radical.

Thermoluminescence responses from europium doped gadolinium oxide

Thermoluminescence signals and morphological studies are reported for a new phosphor ofGd2O3. The phosphor particle material was synthesized by an aerosoltechnique and it is heavily doped with Eu. Annealing at1200 °C increases theluminescence efficiency by ∼1000-fold relative to the as-prepared material. The emission spectra are primarily from the redtransitions of the Eu, but weaker short wavelength emissions can also be detected duringlow temperature thermoluminescence. There are numerous wavelength dependentdifferences between the low temperature thermoluminescence curves. These variations areinterpreted to show that there are a range of defect and luminescence sites in theGd2O3:Eu phosphors. These are associated with the symmetry of the crystal field around theeuropium ion, which is a function of the phase content, i.e. resulting from samplepreparation and annealing. The sites are almost independent in terms of theiremission spectra, but the stability of some sites is enhanced by the presence of Eu sothat the TL peaks appear at higher temperatures than the intrinsic defect TLof the host material. The synthesis of uniform and submicron sized sphericalparticles with nano-clustered inner structure is demonstrated with various analysistechniques (XRPD, FE-SEM and HR-TEM). The effect of processing parameters andpost-annealing treatment is discussed from the viewpoint of different phase formation.

TL of fine-grain samples from quartz-rich archaeological ceramics: Dosimetry using the 110 and [formula omitted] TL peaks

The thermoluminescence characteristics of the 110 and 210 ∘ C peaks of quartz have been successfully exploited to date three rare and ancient Myanmar chess pieces. The particular aspect of this application was that the absorbed dose was evaluated using the polymineral fine-grain fraction with small quantities of the ceramic paste, and that three independent evaluations were possible: two using the pre-dose effect associated with the 110 and 210 ∘ C peaks, and the other using an additive dose technique procedure with 210 ∘ C peak.

Equivalent thermal history [formula omitted] of ferruginous sandstones based on the thermal activation characteristics of quartz

The thermal history of four quartz-rich ochre samples from an Upper Palaeolithic site was studied. This work is based on the changes in thermal activation characteristics (TAC) of the 110 ∘ C TL peak of the quartz inclusions. An isothermal study of a previously unheated sample has highlighted the importance of the duration of annealing on the sensitization of quartz. In fact, the sensitivity change as a function of the duration of annealing is not monotonic. For that reason it seems necessary to consider the “equivalent thermal history” H E rather than an “equivalent temperature”. Isochronal annealing experiments demonstrate that the initial rise of sensitization overestimates the true H E by about 100 ∘ C . Using a geological sample we have thus developed an empirical approach which allows the true H E of artifacts to be determined. Reheating of ochre originally heated in antiquity results in desensitization of the TAC.

Observations of thermal transfer and the slow component of OSL signals from quartz

The thermal transfer optically stimulated luminescence (OSL) signals of bleached samples of sedimentary quartz are investigated using repeated heat/OSL measurement cycles with different heating temperatures ranging from 200 to 360 ∘ C . Under optical stimulation, the thermal transfer OSL decays with stimulation time. A strong correlation is observed between the initial part and the final part of the OSL decay curves. This relationship is dependent on the heating conditions and thermal history of the sample. Our results suggest that the thermal transfer OSL is due to the retrapping of charges that originated from optically insensitive traps by thermal release during heating, and not from the slowly bleached component associated with bleachable traps. Two kinds of OSL traps are involved into the thermal transfer, one is corresponding to the 325 ∘ C TL peak and the other is related to more stable traps. The thermally transferred signals can be distinguished from dose-generated signals by making repeated measurements of thermally transferred OSL decay curves.

Studies of thermal stability of charges associated with thermal transfer of OSL from quartz

In this paper we study optically stimulated luminescence (OSL) signals created by basic thermal transfer. The thermal stabilities of trapped charges associated with the source traps of thermal transfer and their related OSL traps, and trapped holes associated with non-luminescent centres (R centres) were studied for a sedimentary quartz, using isothermal annealing and pulse annealing methods. The thermally transferred charges are mainly from three groups of traps (source traps), shallow, medium and deep traps. Kinetic analysis indicates that the medium and deep source traps have trap depths of ∼1.1 eV and ∼1.5 eV, and lifetimes 7.6 × 105 and 6.0 × 1011 years at 20 °C, respectively. Two kinds of OSL traps, one unstable and the other stable, are identified as accepting charges during thermal transfer. These OSL traps have different thermal stabilities from the main OSL traps, which are associated with the 325 °C TL peak. The results also indicate that the basic thermal transfer related OSL signals perhaps use different R centres from the dose-generated fast bleachable OSL signals.

Luminescence dating of quaternary deposits in geology in Brazil

In the present work, systematic dating by luminescence methods has been done on 50 Quaternary geological samples within the study area of São Paulo State, Brazil. Bleaching experiments showed that residual TL intensity of 375 degrees C peak, of the quartz, was obtained after 10 h of sunlight exposition. Intensities decays of the 325 and 375 degrees C TL peaks can be fitted using second order exponential equation. Paleodose values were evaluated using regeneration methods with multiple aliquots. Samples dated indicate preliminary ages varying from 9 +/- 1 to 935 +/- 130 ka for colluvio-elluvial deposits, and from 17 +/- 2 to 215 +/- 30 ka for alluvial deposits of the study area. They cover four peneplained surfaces shaped during the Quaternary: I (1000-400 ka), II (400-120 ka), III (120-10 ka) and IV (10 ka until today), in decreasing order.

Evaluation of trap parameters associated with thermoluminescence peaks in fired quartz

Dating and retrospective dosimetry are the main applications related to the properties of thermoluminescence of fired quartz. The performance of these techniques can be improved by understanding and characterisation of the traps and luminescence centers responsible for the thermoluminescence emission. In this study, a fired quartz powder sample, extracted from local bricks, is used. Seven overlapping TL peaks are identified by the T m - T stop method. The best peak separation procedure is carried out using the appropriate dose level and pre-heating temperature. For isolated TL peaks located at 100, 202 and 350 ∘ C (as measured with a heating rate of 5 ∘ C s - 1 ), the associated kinetic parameters (activation energy and kinetic order) are determined by three methods: peak shape, whole glow curve and computerised glow curve deconvolution. The results are presented, discussed and compared with those reported in the literature.

Luminescence and ESR properties of Brazilian feldspars

The IRSL and TL responses of three different feldspar crystals have been analysed. TL measurements were taken in the ultraviolet UV (290–370 nm) and the visible VIS (340–610 nm) regions of the spectrum. For the UV region and for a natural sample, peaks were observed at 283, 287 and 310 ∘ C for grey, white and pink crystals, respectively. For samples irradiated after prior preheating, it was noted that TL peaks occurred at about 200 ∘ C for all the samples; irradiation with high doses above 500 Gy induced the formation of one additional peak at 170 ∘ C . The VIS region results were similar to those for the UV. ESR experiments have been developed to verify the influence of radiation and heat treatments on the centres and preliminary results showed great variation in the intensities of [ TiO 4 ] - , Al – O - – Al and Fe 3 + centres.

Red TL of quartz extracted from Chinese loess: Bleachability and saturation dose

The red TL of quartz has been shown to exhibit a much higher saturation dose than that of the UV emission in quartz, and thus has the potential to considerably extend the dating range. Unlike heated materials, in which the luminescence signal has been completely thermally reset, the quartz red TL from Aeolian sediments accumulates on top of a residual signal left after daylight bleaching. The characteristics of this bleaching process must be investigated before any dating attempts can be made. It is demonstrated in this paper that the red TL of quartz extracted from Chinese loess: (1) bleachable by sunlight, but with high residual level. Up to about 40% of the natural signal remains after bleaching in our sample; all of the broad natural TL peak bleaches simultaneously in sunlight; (2) has significant dose-dependent sensitivity change when laboratory doses beyond 1500 Gy are applied; this sensitivity change cannot be corrected for by a test dose; and (3) has a D 0 value of ∼ 550 Gy , much larger than that of optically stimulated luminescence (OSL) ( ∼ 90 Gy ) from the same sample.

Some aspects of phenomenology and kinetics of high temperature thermoluminescence of plagioclase feldspars

Plagioclase feldspars generally display a bright UV TL emission at high temperature (ca 600 ∘ C ). When preheating procedures are used, this TL peak has a very reproducible shape and can be fitted by a single glow-curve with close to second-order kinetics. Nevertheless other experimental evidence, such as the growth of TL intensity with radiation dose or phosphorescence experiments, contradict this simple model. Simulation of experimental data and best-fit techniques indicate that a bell shape model for trap depth distribution is better compatible with the observed data. Furthermore, such a trap distribution model explains some aspects of the behaviour of TL at the onset of saturation. Values of frequency factors and trap depths imply thermal stability for the trapped electrons responsible for high temperature TL.

Defect centres and thermoluminescence in CaSO4:Dy,Ag phosphor

The defect centres formed in the TL phosphor CaSO4:Dy,Ag are studied using the technique of Electron Spin Resonance. The Ag co-doped phosphor exhibits three glow peaks around 130, 220 and 375 degrees C in contrast with the two glow peaks observed in the CaSO4:Dy phosphor at 130 and 220 degrees C at a gamma ray dose of 1Gy. ESR studies show that the additional peak at 375 degrees C correlates with a Ag2+ centre formed due to gamma irradiation and observable only below -170 degrees C. The Ag2+ centre is characterised by an axial g-tensor with principal values g(parallel) = 2.38 and g(perpendicular) = 2.41. ESR studies further indicate that the precursor to a centre observable at low temperature (-170 degrees C) appears to act as the recombination centre for the TL peak at 375 degrees C; this radical is characterised by the g-values g(parallel) = 2.0023 and g(perpendicular) = 2.0038 and is assigned to SO3- radical. It is observed that there is more incorporation of Ag in the CaSO4:Dy system as compared with that in pure CaSO4 system.

Optical absorption, TL and IRSL of basic plagioclase megacrysts from the pinacate (Sonora, Mexico) quaternary alkalic volcanics

The paper presents the first results of an investigation on optical absorption (OA), thermally and infrared stimulated luminescence (TL and IRSL) of the Pinacate plagioclase (labradorite). The OA spectra reveal two bands with maxima at 1.0 and 3.2 eV connected with absorption of the Fe3+ and Fe2+ and IR absorption at wavelengths longer than 2700 nm. The ultraviolet absorption varies exponentially with the photon energy following the 'vitreous' empirical Urbach rule indicating exponential distribution of localised states in the forbidden band. The natural TL is peaked at 700 K. Laboratory beta irradiation creates a very broad TL peak with maximum at 430 K. The change of the 430 K TL peak shape under the thermal cleaning procedure and dark storage after irradiation reveals a monotonous increasing of the activation energy that can be explained by the exponential distribution of traps. The IRSL response is weak and exhibits a typical decay behaviour.

Thermoluminescence Study of Persistent Luminescence Materials: Eu2+- and R3+-Doped Calcium Aluminates, CaAl2O4:Eu2+,R3+

Thermoluminescence properties of the Eu2+-, R3+-doped calcium aluminate materials, CaAl2O4:Eu2+,R3+, were studied above room temperature. The trap depths were estimated with the aid of the preheating and initial rise methods. The seemingly simple glow curve of CaAl2O4:Eu2+ peaking at ca. 80 degrees C was found to correspond to several traps. The Nd3+ and Tm3+ ions, which enhance most the intensity of the high-temperature TL peaks, form the most suitable traps for intense and long-lasting persistent luminescence, too. The location of the 4f and 5d ground levels of the R3+ and R2+ ions were deduced in relation to the band structure of CaAl2O4. No clear correlation was found between the trap depths and the R3+ or R2+ level locations. The traps may thus involve more complex mechanisms than the simple charge transfer to (or from) the R3+ ions. A new persistent luminescence mechanism presented is based on the photoionization of the electrons from Eu2+ to the conduction band followed by the electron trapping to an oxygen vacancy, which is aggregated with a calcium vacancy and a R3+ ion. The migration of the electron from one trap to another and also to the aggregated R3+ ion forming R2+ (or R3+-e-) is then occurring. The reverse process of a release of the electron from traps to Eu2+ will produce the persistent luminescence. The ability of the R3+ ions to trap electrons is probably based on the different reduction potentials and size of the R3+ ions. Hole trapping to a calcium vacancy and/or the R3+ ion may also occur. The mechanism presented can also explain why Na+, Sm3+, and Yb3+ suppress the persistent luminescence.

A CRITICAL APPRAISAL OF THE DETERMINATION OF ACTIVATION ENERGY OF TL PEAKS BY KIRSH METHOD

An attempt has been made to assess critically the suitability of Kirsh method for synthetic TL peaks obtained by solving the set of coupled differential equations. TL peaks represented by three different models namely (i) One Trap One Recombination center (OTOR), (ii) Non-interactive MultiTrap System (NMTS) and (iii) Interactive MultiTrap System (IMTS) have been taken into consideration. It has been found that Kirsh method yields resonably good values of activation energy except for the NMTS model. The validity of the method has been adjudged further by applying it for the determination of activation energies of a number of experimental TL peaks of BeO .

Thallium diagenesis in lacustrine sediments

Dated sediment cores and porewaters from two Canadian Shield lakes, located 40 km from Québec City (L. Tantaré) and 25 km downwind from an important smelter in northwestern Québec (L. Vose), were analyzed for thallium and other geochemical variables. Atmospheric deposition is the only source of anthropogenic Tl to these lakes. The porewater Tl concentration profiles in L. Tantaré display a peak below the sediment-water interface that suggests post-depositional Tl remobilization and transport to the overlying water and deeper sediments; such a dissolved Tl peak occurs just above the sediment-water interface in L. Vose. Modeling the porewater Tl profiles with a diagenetic reaction-transport equation reveals a zone of dissolved Tl production lying above a zone of Tl consumption in L. Tantaré sediments. In contrast, in L. Vose, Tl diffuses across the sediment-water interface from the anoxic hypolimnion and is fixed to the surficial sediments. The localization of the consumption zones, the shape of the dissolved Tl, sulfide and iron profiles, as well as calculations of saturation states are all consistent with the removal of Tl from porewater by co-precipitation with and/or adsorption to Fe sulfides. The concentrations of Tl removed from or added to sediments after their deposition (i.e., diagenetic Tl) amount to up to 36% of measured sediment Tl concentrations. Comparison of the reconstructed historical Tl records with those of polycyclic aromatic hydrocarbons (PAHs) and of Pb originating from coal burning or from smelting activities indicate that coal combustion is the major source of atmospheric Tl to L. Tantaré and that an additional important Tl source to L. Vose is the nearby smelter.