Crushing effects on TL and OSL on quartz: relevance to fault dating

The effect of crushing on the TL and OSL signals in quartz was investigated to examine the feasibility of using OSL and TL for dating of faulted rocks. 275°C TL signals were not reduced by crushing by hand (mortar and pestle), in a pellet die press, or using an automatic mortar and pestle, but the sensitivity of the 100°C TL signal to a test dose decreased in crushed samples. Green light-stimulated OSL signal intensities were not decreased after crushing, but showed strongly increased inter-aliquot variability after crushing. We concluded that OSL and TL in quartz might be useful to characterize the crushing history of quartz in fault rocks, but their usefulness in dating fault events was not evident because we did not find evidence of signal zeroing under the conditions used in this study.     

Luminescence sensitivity changes in quartz as a result of annealing

Retrospective dosimetry using optically stimulated luminescence (OSL) on quartz extracted from (for example) bricks needs to account for strong OSL sensitivity changes that are known to occur depending on the previous thermal treatment of the sample. Non-heated quartz exhibits OSL orders of magnitude less per unit radiation than that for heated material. The reason these temperature-induced sensitivity changes occur in quartz is presently not well understood. This phenomenon is also seen in the related area of luminescence dating in which sedimentary quartz and quartz from heated archaeological samples show very different OSL sensitivities. In this paper we report on studies of the effects of high temperature annealing on the OSL and phototransferred TL (PTTL) signals from sedimentary and synthetic quartz. A dramatic enhancement of both OSL and PTTL sensitivity was found especially in the temperature range 500–800°C. Computer simulations of the possible effects are shown to produce data that agree in all essential details with the experimental observations. It is further demonstrated that the enhanced OSL sensitivity as a function of annealing temperature is not a pre-dose effect.     

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.     

OSL from BeO ceramics: new observations from an old material

In BeO ceramics, exposed to ionizing radiation, an intense OSL signal was observed. The properties of the signal and its behavior under various experimental conditions were investigated. It was found that the OSL signal is a composite signal and exhibits strong thermal quenching. The quenching energy was estimated as 0.5 eV. The excitation spectrum of the OSL signal was obtained as a broad peak in the region 420–550 nm with maximum around 435 nm. The possible correlation between the OSL signal and the peaks in the TL glow curve was also examined. It was interesting to observe that the highly light sensitive TL peak near 220°C does not contribute to the OSL signal. The OSL signal was found to originate from a trap near 340°C.

To check the possibility of using the material for radiation dosimetry the dose response and thermal stability of the OSL signal were also investigated. The dose response was found to be quite linear up to 10 Gy. The thermal activation energy of the OSL trap was determined as 1.7 eV using isothermal annealing and heating rate methods thus proving the suitability for dosimetry.     

The timing of OSL sensitivity changes in a natural quartz

The timing of 110°C thermoluminescence (TL) and optically stimulated luminescence (OSL) sensitivity changes is explored using a natural (aeolian) quartz sample from Australia that was previously found to exhibit marked dose-dependent sensitivity change. The changes occur asynchronously; the 110°C TL sensitivity changes after dosing plus pre-heating, whereas the OSL sensitivity changes (proportionately with dose) after optical bleaching. Although the magnitude and saturation characteristics of the sensitivity changes are found to be similar, their non-synchronicity negates a direct link between the phenomena. Implications of these results for dating procedures are discussed. In particular, the results indicate that a single aliquot additive dose procedure similar to that developed for coarse-grained potassium feldspar should be possible for some quartz samples.     

TL and PTTL in natural fluorite previously irradiated with gamma rays and heavy ions

The effect of annealing temperature on the phototransfer thermoluminescence (PTTL) signal was studied to determine the appropriate annealing temperature for treating the natural powder before irradiation. The temperatures used to anneal virgin natural fluorite samples (only natural dose without giving the samples any artificial doses) were 150, 250, 350, 450, 550, 650 and 750°C for a duration of 1 h in each case. The results show that the PTTL response did not change for anneal temperatures up to 450°C, but at higher temperatures the signal decreased rapidly. The height of the 90°C peak decreased by two orders of magnitude as the anneal temperature increased from 450 to 750°C, whilst the height of the 180°C peak decreased by three orders of magnitude between the same two annealing temperatures. In order to investigate the effect of previous gamma rays and heavy ion irradiation on thermoluminescence (TL) and PTTL signals, powdered samples of natural fluorite from Cornwall, England, were annealed at 500°C and then irradiated (at GSI, Darmstadt, Germany) with ¹⁶¹Dy ions of energy 13 Mev/n; the range of fluences used was from 10⁴ to 10¹² ion cm⁻². Identical samples were given gamma doses in the range 1 Gy to 2.6 × 10⁴ Gy in order to compare the effects of gamma rays and heavy ions. The sensitivities of TL and PTTL were studied by giving the samples a gamma test dose of 1 Gy after annealing the samples at 500°C for 30 min in order to eliminate the TL resulting from previous gamma or heavy ion irradiation.     

Kinetics of red, blue and UV thermoluminescence and optically-stimulated luminescence from quartz

The duration over which charge is retained at trapping sites is of fundamental importance for trapped electron dating. Here, we report measurements of the kinetic parameters of the prominent thermoluminescence (TL) glow peaks of quartz, and of the optically-stimulated luminescence (OSL) signal from quartz utilised for optical dating. The similarity in trapping lifetimes of the 325°C TL peak and the dominant component of the OSL signal are taken as further support for the hypothesis of their common origin in the same trapped electron population.     

The TL and room temperature OSL properties of the glow peak at 110 °C in natural milky quartz: A case study

The LM–OSL signal of quartz, while measured at room temperature, is dominated by an intermediate, broad and intense OSL component, so that its contribution and general characteristics are derived very accurately. Through a series of dose–response, bleaching and thermal decay at room temperature experiments, in conjunction with curve fitting studies, a component resolved analysis is carried out studying the correlation between this specific component, termed as LM–OSL component C₂ and the 110 °C TL glow peak in quartz. The dose–response of these two luminescence components behaves exactly similar being linear at low doses and saturating at almost 100 Gy. Both signals decay exponentially under illumination, providing identical optical detrapping cross-section values. Residual of both luminescence signals after thermal decay at room temperature follows an exponential law, yielding similar mean half-lives. All previous luminescence features provide strong evidence for the electron trap being the same for both the 110 °C TL trap and the LM–OSL component C₂. The results of the present work are very promising and clearly support the possibility of extrapolating the TL pre-dose methodology to the OSL pre-dose effect using only the LM–OSL component C₂.     

Effects of annealing on TL sensitivity of granitic quartz

A TL sensitivity change can usually be observed after the quartz sample is heated to a high temperature. The change of 110°C TL peak or PTTL was reported to be an increase in many studies. The change of TL sensitivity of other TL peaks, mainly 150 and 375°C, with annealing treatments was demonstrated in this study. Two types of TL sensitivities in granitic quartz were found. One type is the low temperature TL sensitivity (<250°C) which increases with annealing time and temperature. Another type is the high temperature TL sensitivity (>250°C) which usually decreases after annealing. If the TL sensitivity is a measure of the population of associated TL traps, the trap population is a potential geochronometer to date a cooling age of a granite host.     

Application of the single-aliquot regenerative-dose protocol to the 375°C quartz TL signal

We report on investigations into the suitability of a single-aliquot regenerative-dose (SAR) protocol applied to the isothermal TL signal obtained from quartz held at 330°C. Samples are first thermally and optically pretreated to remove any signal from the 325°C TL trap. It is shown that the regenerated TL decay curve has the same shape as the natural one, and that recuperation is negligible. Examination of the TL glow curve before and after isothermal measurement suggests that the isothermal signal comes mainly from the 375°C TL peak, and a pulse anneal experiment is used to confirm this. This signal is bleached by simulated sunlight, with a fast component (making up about 60% of the total natural signal) bleaching about 30 times faster than a slower component. The SAR protocol is then applied to 9 samples from various depositional environments, and it is shown that the resulting data satisfy the internal checks of reliability, i.e., independence of prior treatment, and absence of recuperation. Examination of the sensitivity-corrected growth curve shows that the applicable age range for this signal may be only slightly greater than that from the OSL signal derived from the 325°C peak. This limited advantage is offset by the much greater difficulty of bleaching.     

Relative response of TL and component-resolved OSL to alpha and beta radiations in annealed sedimentary quartz

Knowledge of the relative luminescence response to alpha and beta radiation is very important in TL and OSL dating. In the present study the relative alpha to beta response is studied in a sedimentary quartz sample, previously fired at 900 °C for 1 h, in the dose region between 1 and 128 Gy, for both thermoluminescence (TL) and linearly modulated optically stimulated luminescence (LM – OSL). The LM – OSL measurements were performed at room temperature and at 125 °C. All OSL signals were deconvolved into their individual components. Comparison of OSL curves after alpha and beta irradiation strongly supports that quartz OSL components follow first order kinetics in both cases. In the case of TL, the relative alpha to beta response is found to be very different for each TL glow-peak, but it does not depend strongly on irradiation dose. In the case of LM – OSL measurements, it is found that the relative behaviour of the alpha to beta response is different for three distinct regions, namely the fast OSL component, the region of medium OSL component originating from the TL glow-peak at 110 °C when stimulation takes place at room temperature and finally the region of slow OSL component. Following stimulation at ambient temperature, the relative alpha to beta response of all components was not observed to depend significantly on dose, with the value of ratio being 0.03 and a tendency to decrease with increasing dose. However, in the case of measurements performed at 125 °C, the relative response of the fast components is much enhanced, and for the remaining components it increases with increasing dose. Special care must be taken to examine the relative alpha to beta response of the fast component at 125 °C which contrasts the relative response of the TL peak at ca. 325 °C. The implications for the dating of annealed quartz are also briefly discussed.     

Investigating quartz optically stimulated luminescence dose–response curves at high doses

Despite the general expectation that optically stimulated luminescence (OSL) growth should be described by a simple saturating exponential function, an additional high dose component is often reported in the dose response of quartz. Although often reported as linear, it appears that this response is the early expression of a second saturating exponential. While some studies using equivalent doses that fall in this high dose region have produced ages that correlate well with independent dating, others report that it results in unreliable age determinations. Two fine grain sedimentary quartz samples that display such a response were used to investigate the origin of this additional high dose component: three experiments were conducted to examine their dose–response up to >1000 Gy. The high dose rates provided by laboratory irradiation were found not to induce a sensitivity change in the response to a subsequent test dose, with the latter not being significantly different from those generated following naturally acquired doses. The relative percentage contributions of the fast and medium OSL components remained fixed throughout the dose–response curve, suggesting that the electron traps that give rise to the initial OSL do not change with dose. An attempt was made to investigate a change in luminescence centre recombination probability by monitoring the depletion of the ‘325 °C’ thermoluminescence (TL) during the optical stimulation that would result in depletion of the OSL signal. The emissions measured through both the conventional ultraviolet (UV), and a longer wavelength violet/blue (VB) window, displayed similar relative growth with dose, although it was not possible to resolve the origin of the VB emissions. No evidence was found to indicate whether the additional component at high doses occurs naturally or is a product of laboratory treatment. However, it appears that these samples display an increased sensitivity of quartz OSL to high doses that is not recorded by the sensitivity to a subsequent test dose, and which results in a change in the sensitivity-corrected dose–response curve.     

LiMgPO_4:Tm,Tb的热释光和光释光陷阱参数

采用高温固相法合成了LiMgPO_4:Tm,Tb粉末样品,测定了热释光陷阱参数激发能E和频率因子s.用脉冲退火和多次退火方法研究了其光释光陷阱参数E和s,并与用多速法得到的热释光的结果进行了比较.对不同β射线剂量照射的样品发光曲线的研究表明,300°C高温峰属于一级动力学发光峰.通过对热释光和光释光陷阱的相关性研究表明,经200°C预热的热释光信号(对应于300°C高温峰)和光释光信号很有可能来自于同一深度的陷阱.     

Investigating the thermally transferred optically stimulated luminescence source trap in fired geological quartz

The pre-dosed thermoluminescence (TL) emission of quartz has been found to be useful in retrospective dosimetry and archaeometry. Though the pre-dosed optically stimulated luminescence (OSL) and TL emissions have been reported to be similar, the former has been found to be un-reliable for the equivalent dose estimation. As this measurement protocol involves thermal heating at around 400 °C, the work reported in this paper investigated the influence of this heating on the OSL using fired specimens from various regions. The results suggested that the discrepancy in the behaviour of two emissions is caused by the presence of the thermally transferred optically stimulated luminescence (TT-OSL) induced by thermal-activation involved in the pre-dose treatment. This transferred signal was observed to be very significant in the case of samples containing a prominent higher-temperature TL peak at ∼375 °C. The characterization of this signal based on (i) the nature of the glow curves, (ii) thermal-annealing of the OSL trap, (iii) observation of the TT-OSL, (iv) bleaching of the source trap and (v) the correlation between TL and OSL seems to suggest that the trap corresponding to this TL peak is the source trap in the TT-OSL emission mechanism.     

Correlation of optically and thermally stimulated luminescence of natural fluorite pellets

Natural fluorite (CaF₂), a dosimetric material of large usage, presents Thermoluminescence (TL) and Optically Stimulated Luminescence (OSL). This study examined the behavior of TL and OSL (stimulated with Blue LEDs) signals from the Brazilian natural fluorite pellets with NaCl as binding agent, as well as their correlations, in order to study and optimize the dosimetric process with this material. A series of experiments were conducted, basically with thermal treatments before OSL acquisition, and optical bleaching before TL readout. The role of NaCl in the TL and OSL emission was investigated. It was observed that natural CaF₂ TL signal is still ample to be used in dosimetric applications, as dose re-assessment in personal dosimetry after an OSL measurement. Also it was verified that the fluorite OSL signal is extinguished by a 350 °C heating and that NaCl has no contribution to the stable part of the OSL signal.     

不同退火温度的Al_2O_3:C薄膜热释光和光释光性能

α-Al_2O_3:C晶体的热释光和光释光性能优越,但其制备要求高,需高温和高还原气氛.与α-Al_2O_3:C晶体性能接近的α-Al_2O_3:C陶瓷,热释光峰不单一.本文采用两次阳极氧化法在0.5 mol/L的草酸溶液中5℃恒温制备高度均匀有序的多孔Al_2O_3:C薄膜,主要研究不同退火温度对其热释光和光释光特性的影响.结果表明,经不同温度退火后的Al_2O_3:C薄膜均为非晶结构;不同退火温度的Al_2O_3:C薄膜热释光的主发光峰约在310℃左右,符合通用级动力学模型.600℃退火后的Al_2O_3:C薄膜热释光灵敏度最强,其热释光剂量曲线在1-10 Gy范围内具有很好的线性响应,在剂量10-120 Gy范围内出现超线性响应;在相同的辐照剂量下,随着退火温度的升高(≤600℃)光释光的初始发光强度逐渐增强.不同退火温度的Al_2O_3:C薄膜光释光衰减曲线都呈典型的指数衰减且快衰减速率相比α-Al_2O_3:C晶体显著加快.600℃退火后的Al_2O_3:C薄膜光释光灵敏度最强,其光释光剂量响应曲线在1-200 Gy整体上都具有很好的剂量线性关系.与热释光相比,Al_2O_3:C薄膜的光释光具有更宽的线性剂量响应范围.此研究为Al_2O_3:C薄膜作为光释光辐射剂量材料做出了有益的探索.     

The ‘110°C’ TL peak in synthetic quartz

The thermoluminescence (TL) of synthetic quartz has been investigated in the temperature region 275–475 K. These measurements have revealed a more complicated structure of the 110°C TL peak and thermal activation energies and frequency factors have been estimated for a number of peaks within the glow curve. The results obtained after annealing samples in different atmospheres indicate that oxygen-related defects play an important role in the luminescence process, involving both the charge traps and recombination centres.     

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 production in the single-aliquot regenerative dose protocol

When using a single-aliquot regenerative dose (SAR) protocol for luminescence dating of sedimentary quartz grains, the fundamental assumption is that the sensitivity of the optically stimulated luminescence (OSL) produced by the regenerative doses can be monitored by their following test dose OSL response. Using well-bleached coarse quartz grains, OSL production in a SAR protocol was studied in detail when dose response curves were constructed using both single and multiple aliquot regenerative dose procedures. During application of the SAR protocol, two preheats are applied, each ahead of an OSL measurement that is produced by the regenerative dose and test dose, respectively. It is shown that sensitivity changes caused by heating were well corrected for using the OSL response to the test dose. However, these preheats are shown to result in thermally stimulated OSL signals that contribute both to the OSL response from the regenerative doses used to construct the dose response curve and to the OSL response from the test dose used to monitor OSL sensitivity changes as the quartz grains are repeatedly measured. A simple test is proposed to identify the contribution of the latter signal.     

Absorbed dose evaluations in retrospective dosimetry: methodological developments using quartz

Dose evaluation procedures based on luminescence techniques were applied to 50 quartz samples extracted from bricks that had been obtained from populated or partly populated settlements in Russia and Ukraine downwind of the Chernobyl NPP. Determinations of accrued dose in the range 30–300 mGy were obtained using TL (210°C TL and pre-dose) and OSL (single and multiple aliquot) procedures. Overall, good inter-laboratory concordance of dose evaluations was achieved, with a variance (1σ) of ±10 mGy for the samples examined.