Influence of pre-measurement thermal treatment on OSL of synthetic quartz measured at room temperature

Much effort has been made to study the influence of pre-measurement thermal treatment and ionizing radiation on quartz specimens owing to its use in a large number of applications. Optically stimulated luminescence (OSL) being a structured and sensitive phenomenon promises to correlate the responsible color center and luminescence emission. OSL studies on quartz with such conditions can reveal many significant results.The aim of the present investigation is to understand the effect of annealing temperature on OSL characteristics of synthetic quartz recorded at room temperature. At identical annealing duration and β-dose, the shape of OSL decay curve remains non-exponential; when specimens annealed at lower temperature (∼400 °C). The shape of decay curve changes to exponential in nature along with rise in OSL intensity when the specimen was given higher temperature of annealing (>400 °C). The effects of such protocol on pattern of OSL sensitivity as well as area under the OSL decay curve are also presented here. The presence of shallow traps, when OSL decay curve was recorded at room temperature seems to be responsible for the changes in OSL pattern. The influence of shallow traps is attributed to non-exponential decay of OSL recorded at room temperature.     

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.     

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.     

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.     

Effect of high-dose irradiation on the optically stimulated luminescence of Al2O3:C

This paper examines the effect of high-dose irradiation on the optically stimulated luminescence (OSL) of Al2O3:C, principally on the shape of the OSL decay curve and on the OSL sensitivity. The effect of the degree of deep trap filling on the OSL was also studied by monitoring the sensitivity changes after doses of beta irradiation and after step-annealing of samples previously irradiated with high doses. The OSL response to dose shows a linear-supralinear-saturation behavior, with a decrease in the response for doses higher than those required for saturation. This behavior correlates with the sensitivity changes observed in the samples annealed only to 773 K, which show sensitization for doses up to 20-50 Gy and desensitization for higher doses. Data from the step-annealing study leads to the suggestion that the sensitization is caused by the filling of deep electron traps, which become thermally unstable at 1100-1200 K, whereas the desensitization is caused by the filling of deep hole traps, which become thermally unstable at 800-875 K, along with a concomitant decrease in the concentration of recombination centers (F+ -centers). Changes in the shape of the OSL decay curves are also observed at high doses, the decay becoming faster as the dose increases. These changes in the OSL decay curves are discussed in terms of multiple overlapping components, each characterized by different photoionization cross-sections. However, using numerical solutions of the rate equations for a simple model consisting of a main trap and a recombination center, it is shown that the kinetics of OSL process may also be partially responsible for the changes in the OSL curves at high doses in Al2O3:C. Finally, the implication of these results for the dosimetry of heavy charged particles is discussed.     

Optically stimulated luminescence (OSL) of dental enamel for retrospective assessment of radiation exposure

This paper briefly reviews the optically stimulated luminescence (OSL) properties of dental enamel and discusses the potential and challenges of OSL for filling the technology gap in biodosimetry required for medical triage following a radiological/nuclear accident or terrorist event. The OSL technique uses light to stimulate a radiation-induced luminescence signal from materials previously exposed to ionizing radiation. This luminescence originates from radiation-induced defects in insulating crystals and is proportional to the absorbed dose of ionizing radiation. In our research conducted to date, we focused on fundamental investigations of the OSL properties of dental enamel using extracted teeth and tabletop OSL readers. The objective was to obtain information to support the development of the necessary instrumentation for retrospective dosimetry using dental enamel in laboratory, or for in situ and non-invasive accident dosimetry using dental enamel in emergency triage. An OSL signal from human dental enamel was detected using blue, green, or IR stimulation. Blue/green stimulation associated with UV emission detection seems to be the most appropriate combination in the sense that there is no signal from un-irradiated samples and the shape of the OSL decay is clear. Improvements in the minimum detection level were achieved by incorporating an ellipsoidal mirror in the OSL system to maximize light collection. Other possibilities to improve the sensitivity and research steps necessary to establish the feasibility of the technique for retrospective assessment of radiation exposure are also discussed.     

Luminescence properties of BeO optically stimulated luminescence (OSL) detectors

The objective of this work is to investigate basic luminescence properties of BeO optically stimulated luminescence (OSL) detectors, including the OSL emission and stimulation spectrum, the lifetime of the luminescence centers contributing to the OSL signal, and the temperature dependence of the luminescence lifetime and of the luminescence efficiency. The OSL stimulation spectrum shows a continuous increase in OSL intensity with decreasing stimulation wavelength. The emission spectrum indicates two OSL emission bands at ～310 nm and ～370 nm, the latter being the dominant OSL emission band. We also observed that the luminescence centers associated with the OSL signal are strongly quenched above room temperature, resulting in a reduction in luminescence lifetime from ～27 μs at room temperature down to ～800 ns at 140 °C. The activation energy for non-radiative decay of the luminescence center was determined to be E = (0.568 ± 0.023) eV. The ～27 μs luminescence lifetime observed for BeO indicate that POSL technique may be used to improve the signal-to-noise ratio using stimulation pulses of the order of microseconds. The information obtained in this study may help further optimize the BeO dosimetry systems and provide guidance on the timing parameters to be used for POSL measurements of this material.     

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.     

Time-resolved OSL studies on BeO ceramics

Time-Resolved Optically Stimulated Luminescence (TR-OSL) from BeO ceramics was investigated using a blue laser (445 nm) as stimulation light source. It was observed that, at relatively low dose levels (up to ∼25 Gy) the TR-OSL decay curve can be approximated with a single exponential decay function with a lifetime of ∼26 μs at room temperature. Beyond 25 Gy a new decay component with a lifetime of a ∼2 μs was observed in addition to the ∼26 μs component. Thermal stability, radiation dose response, optical bleaching, measurement temperature dependence of the components of the TR-OSL signal were investigated in detail. As result of these studies, a new OSL component which becomes unstable after 150 °C was observed. OSL decay rate of this component was found to be higher than the one which becomes unstable after 300 °C. In order to obtain information about the temperature dependence of the luminescence efficiency, luminescence emission lifetime was determined in the temperature range from 30 to 130 °C with 10 °C steps. Using the temperature dependence of the lifetime, thermal quenching energy was determined to be around 0.56 eV for the 26 μs component. For the ∼2 μs component an enhancement in the component intensity was observed pointing to a thermally assisted process with activation energy of 0.15 eV.     

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.     

Study of sensitivity change of OSL signals from quartz and feldspars as a function of preheat temperature

Optically stimulated luminescence (OSL) signals from feldspar and quartz samples were studied using infrared (860 nm) and green light (420–575 nm) stimulation. A serious problem connected with the regeneration technique used for dating is associated with a change of OSL sensitivity to radiation in the course of the measurement process. A typical effect seen is a large increase of the apparent strength of our beta source when calibrated against a gamma source. If the regeneration procedure is used, it is shown that the sensitivity increases up to 50% during the measurement process and as a result, the equivalent dose (ED) would be underestimated. A study of sensitivity changes in feldspars and quartz was carried out with emphasis on the effect of preheat and annealing on the OSL signal. Measurement results obtained are presented, and possible elimination of errors in dating caused by sensitivity changes is discussed.     

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.     

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.     

OSL and TSL interrelations in SrSO4:Eu

Thermoluminescence (TL), dose-dependence of TL, optically stimulated luminescence (OSL), and EPR of Eu-doped strontium sulphate are studied. Eu enters the host lattice in 2+ charge state and does not change the charge state during energy storage and release. OSL disappears during pulse-step annealing of excited luminophor at the temperatures corresponding to dosimetric TL peak. Dosimetric TL peak can be destroyed by a continuous optical stimulation of excited sample. Ionizing radiation creates radiation defects in the host lattice, with the ionized sulphate anions being stable hole centres well above room temperature. Optical stimulation in the blue band (460–470 nm) causes the captured holes to be transported to the luminescence centres, similarly acts the heating of luminophor. The model of energy storage and release is discussed.     

强辐照场下氟化铈（CeF3）的荧光特性

研究了国产ＣｅＦ３晶体在４．３ｋＧｙ的辐照剂量下的荧光特性及其在室温下辐照损伤的恢复性能，测量显示辐照对荧光光谱和衰减时间不产生影响，但色心的形成使晶体透光性能变差。对辐照损伤的机理进行了探讨。     

The Dependence of IRSL Intensity on Radiation Dose for Samples of Chlorides Contained in Feldspars

The intensity of the luminescence generally increases with radiation dose and measurement of these phenomena can be used to characterise the degree of dependence on beta doses. In this study, in order to test whether this is a significant problem on the optically stimulated luminescence (OSL) studies, the radiation dose response of the OSL signal from samples of chlorides contained in feldspars have been investigated by irradiating the samples with beta doses. The infrared-emitting diodes were used with a wavelength of (880±80) nm, and an IRSL (infrared stimulated luminescence) intensity parametres, m, was described and found m = 1±0.03.     

不同粒径α-Al2O3:C晶态粉体热释光和光释光特性

本文探讨了α -Al₂O₃:C晶态粉体的辐照剂量效应, 使用RisøTL/OSL-DA-15 型热释光和光释光仪研究其热释光和光释光特性, 结果发现, 相同粒径的α-Al₂O₃:C晶态粉体具有单一热释光峰, 且随着辐照剂量的增加热释光强度不断增加, 但热释光峰位置保持不变, 符合一级动力学模型; 而在相同的辐照剂量和测试条件下, 随着α -Al₂O₃:C晶态粉体粒径的减小, 其热释光强度先增强后减弱, 热释光峰却逐渐增加至趋于稳定, 表明粒度为40—60 μ的α -Al₂O₃:C晶态粉体具有最佳的热释光效应. 同时α -Al₂O₃:C晶态粉体的光释光特性的研究发现, 其光释光曲线具有典型的指数衰减特征, 粒径对其光释光强度和衰减速率的影响符合浅电子陷阱能级理论.     

OSL and TL in TLD-100 following alpha and beta irradiation: Application to mixed-field radiation dosimetry

The optically stimulated luminescence (OSL) of LiF:Mg,Ti (TLD-100) following irradiation by beta and alpha particles was investigated by measurement of the excitation and emission spectra of OSL and comparison with thermoluminescence (TL) characteristics. The OSL excitation spectra of all the samples following both beta and alpha irradiation are very similar.Identical emission bands with very similar relative intensities following both beta irradiation and alpha particle irradiation have been recorded in the OSL induced in nominally pure LiF mono and TLD-100 polycrystals. The identical excitation and emission bands in the doped and pure crystals are strong evidence indicating that the observed OSL is due to an intrinsic trapping structure. The OSL has indeed been previously attributed to F₂ centers and F₃⁺ centers.The preferential excitation of OSL compared to TL following high ionisation density (HID) alpha irradiation is naturally explained via the identification of OSL with the “two-hit” F₂ or F₃⁺ center, whereas the major component of composite TL glow peak 5 is believed to arise from a “one-hit” complex defect. This discovery allows near-total discrimination between HID radiation and low ionisation density (LID) radiation and may have significant potential in mixed-field radiation dosimetry.     

SrSO4:Eu磷光体的光释光特性

研究了通过掺杂得到的SrSO4:Eu(01mol%)的粉末样品的光释光(OSL)特性.用90Sr的β射线辐照0116—116kGy后，测定了恒定光源激发的光释光发光曲线(CW-OSL)和线性光源激发的光释光发光曲线(LW-OSL)，对发光曲线分析均得到了四种陷阱成分.采用复合作用响应函数得到SrSO4:Eu辐射剂量响应为线性-亚线性.测量了温度对OSL信号的影响，结果表明OSL信号的温度稳定性很好，最灵敏读出温度约为180℃，说明这时OSL信号来自热激发和光激发的共同作用.用60Coγ辐照100Gy后，测量了热释光(TL)三维光谱，确定了发光波长主要位于375nm，可以确定这是来自于Eu2+能级跃迁的发光. 关键词： 光释光 热释光 SrSO4:Eu     

OSL and TL retrospective dosimetry with a fluorapatite glass-ceramic used for dental restorations

Optically Stimulated Luminescence (OSL) and Thermoluminescence (TL) properties of a fluorapatite glass-ceramic have been investigated, with a view to developing a dose assessment technique for medical triage following unplanned exposures of individuals to ionizing radiation. The ceramic is an innovative material used in dental prostheses and restorations. It is strongly sensitive to radiation and the intensity of both the OSL and TL signals are proportional to the absorbed radiation dose. We focused on the optimization of the measuring procedure and investigated characteristics such as reproducibility, fading, minimum detectable dose (MDD), dose response and photon energy response of TL and OSL signals. The dental ceramic exhibited very good reproducibility (<5% at 2σ level) when measured and a linear dose response for a wide range of doses (50 mGy–20 Gy). The MDD values for the samples investigated were ∼5 mGy. The material is not tissue equivalent and the OSL and TL signals are strongly dependent on incident photon energy. Both the luminescence signals exhibited significant fading during the first few hours after irradiation. Its rate was dependent on the parameters of measurement. The results indicate that the material can be used for the purposes of accident dosimetry, however, the fading and photon energy response have to be properly corrected for a reliable dose assessment.