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Isothermal thermoluminescence (ITL) and thermoluminescence (TL) signals from quartz were studied. A single aliquot regenerative dose protocol has been applied for ITL D e determination (SAR-ITL). In the SAR-ITL protocol, the preheat condition was a cutheat to 10 °C higher than measurement temperature. The test dose was approximate to the expected D e , and a 450 °C heat was given at end of each cycle to minimize signal build-up. Based on signals strength and dose recovery test, temperatures of 235 and 255 °C were selected for the ITL D e measurement. A multiple aliquots regenerative protocol has been applied for TL D e determination (MAR-TL). The preheat procedure was a cutheat of 235 °C and a second glow TL of 175 Gy was used for normalization. The sensitivity change of first heating to 450 °C was negligible, supported by comparison between additive and regenerative dose growth curves. Based on the natural TL signal and preheat condition studies, D e values at temperatures of 250–330 °C were used for thermochronological study. These two protocols were applied to rock samples collected at different elevations from Nujiang River (also called Salween River) valley slope. The SAR-ITL gave D e results consistent with the MAR-TL at temperatures of 40–50 °C higher. The results clearly demonstrate the differences in the thermal histories between the analyzed samples. The SAR-ITL and MAR-TL protocols were both found to be suitable for application in thermochronology.

Optically stimulated luminescence (OSL) ages can determine a wide range of geological events or processes, such as the timing of sediment deposition, the exposure duration of a rock surface, or the cooling rate of bedrock. The accuracy of OSL dating critically depends on our capability to describe the growth and decay of laboratory-regenerated luminescence signals. Here we review a selection of common models describing the response of infrared stimulated luminescence (IRSL) of feldspar to constant radiation and temperature as administered in the laboratory. We use this opportunity to introduce a general-order kinetic model that successfully captures the behaviour of different materials and experimental conditions with a minimum of model parameters, and thus appears suitable for future application and validation in natural environments. Finally, we evaluate all the presented models by their ability to accurately describe a recently published feldspar multi-elevated temperature post-IR IRSL (MET-pIRIR) dataset, and highlight each model's strengths and shortfalls.

In luminescence measurements of potassium-feldspar (K-feldspar), both infrared (IR) and blue light (BL) can be used as stimulation sources. Component analysis suggests that the blue light stimulated luminescence (BLSL) measured at 60 °C from K-feldspar can be fitted using three components, namely fast, medium and slow. In order to explore the relationship between the origin of the infrared stimulated luminescence (IRSL) signal and the different components of the BLSL, five sets of experiments were conducted, namely post-IR BLSL (pIR-BLSL), post-BL IRSL (pBL-IRSL), pulse annealing tests, dose response and laboratory fading rate tests. It is observed that most of the IRSL signal can be bleached by BL, while the BLSL signal can only be partially bleached by the IR. The sources for IRSL are mainly associated with the fast and medium components of the BLSL signal.

Optically stimulated luminescence (OSL) dating has been applied to quartz grains extracted from a sedimentary layer containing stone tools from the bank of Salawusu River, Mu Us desert in central China. Severe age underestimation was observed by applying the single-aliquot regenerative dose (SAR) dating method when compared with the isochron infrared stimulated luminescence (iIRSL) dating results using potassium-rich feldspar grains of different grain sizes. Preheating plateau and dose recovery tests suggest that the SAR protocol is robust for this sample. Component resolving indicates that the OSL signals were dominated by the fast component. However, the fast component is thermally unstable as shown by pulse-annealing measurements and single-grain study. This leads to OSL age underestimation. To overcome this problem, a method was proposed by combining equivalent dose (De) determination and pulse-annealing experiments using single-grain measurements to select only those grains with the thermally stable signals. For those quartz grains with thermally stable OSL signals, the ages obtained are consistent with iIRSL results.

The thermal stability of the infrared stimulated luminescence (IRSL) signal measured at 50 °C as a function of IR stimulation time was investigated using KF grains extracted from sediments from central China. A dependence of thermal stability of IRSL signal on IR stimulation time and stimulation temperature were observed in pulse annealing studies. Relatively lower thermal stability is given by the initial part of the IRSL measured at 50 °C, than the later part of IRSL curve. Based on these observations, the thermal stability of the post-IR IRSL signal stimulated at elevated temperatures (100–200 °C) was also investigated. It was found that at least two groups of traps (shallow and deep) are associated with the IRSL and post-IR IRSL signals. The IRSL signal obtained at 50 °C is mainly from the shallow traps while the post-IR IRSL obtained at elevated temperatures is mainly from the deep traps. The kinetics parameters obtained using pulse annealing test indicate that the shallow IRSL traps are probably associated with the ∼300–350 °C TL peak and the deep traps are probably associated with the ∼400 °C TL peak. The shallow traps (∼350 °C TL peak) are associated with those easy-to-fade traps and the deep traps (∼400 °C TL peak) are associated with hard-to-fade traps.

This paper presents the study of infrared stimulated luminescence (IRSL) at elevated temperatures from an annealed quartz sample. Trap parameters of the IRSL signals were measured using pulse-annealing experiments with different heating rates and compared with the equivalent results for the optically stimulated luminescence (OSL) obtained using blue light emitting diodes as the stimulation source. The results demonstrate that the IRSL signal comprises of only one component which is associated with the rapidly bleachable OSL traps; the OSL of this annealed quartz contains several components with different bleaching rates and different thermal stabilities. The lifetimes of the IRSL and OSL signals were estimated. A protocol for quartz dating using IRSL signals is proposed and is tested by recovery of given doses.

The equivalent doses of K-feldspar grains in a range of grain sizes from 90 to 250 μ m diameter were measured using a single-aliquot regenerative-dose protocol for the infrared stimulated luminescence (IRSL) signals for two samples of desert sand. The equivalent doses for each sample were compared with that for the 125 – 150 μ m grains of quartz from the same samples. The results suggested that the K-feldspar equivalent doses were underestimated because of anomalous fading. Measurements of the decay of the IRSL signals following laboratory irradiation for these two samples, and an additional one from a previously published isochron study, showed anomalous fading during the period of laboratory storage. The decay rate was about 3% per decade for all samples and was independent of the grain size used. Using plots of equivalent doses for K-feldspars as a function of their calculated internal dose rate, and the quartz equivalent dose as a function of grain size, it was concluded that the IRSL signal derived from the internal dose rate had not faded over the 13,000 years that had elapsed since the grains were deposited.

Overestimation of equivalent dose ( D e ) values due to thermal transfer was observed for quartz when using the single-aliquot regenerative-dose protocol (SAR) to recover a small known dose (1.74 Gy) given after an optical bleach. Both the fast and medium components resulted in overestimation, with the effect being larger for the medium component and the effect could be seen in D e ( t ) plot as stimulation time increased. The dose-generated OSL signal can be distinguished from the thermally transferred signal based on the linear relationship between the initial and final parts of the thermally transferred OSL curves. A method is proposed to correct for thermal-transfer effects using the OSL signals measured in repeated heat/OSL cycles incorporated into the SAR protocol. This approach was applied to artificially irradiated and optically bleached samples, and it was found that the thermal-transfer effects can be removed when using only a single aliquot. In dose recovery tests, the known dose (1.74 Gy) could be obtained using this approach and a value of 0.074 ± 0.026 Gy was obtained for optically bleached aliquots.

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.

A method is described for equivalent dose determination using the linearly modulated optically stimulated luminescence (LM-OSL) signal from quartz. After analysis of the LM-OSL curves, only the fast component from quartz is used for equivalent dose calculation. The results of applying the method to purified quartz and to grains without mineral separation are presented.

In equivalent dose ( D e ) determination of quartz using the single aliquot regenerative dose (SAR) technique, it is commonly observed that the D e values are strongly dependent on the stimulation time for some well bleached samples. Such dependence is not controlled by the degree of recuperation of the optically stimulated luminescence (OSL) signals. Instead, this behavior is interpreted as being due to the medium component being thermally unstable for these samples and giving a lower D e value than the fast component. An alternative method is described for the D e determination of samples that exhibit such a phenomenon.

The concentrations of radioactive elements in K-feldspar grains were studied using electron micro-probe for potassium (K) content and inductively coupled plasma mass spectrometer (ICP-MS) for uranium (U), thorium (Th) and rubidium (Rb) contents. The K content of individual grains is 13–14%. The U, Th and Rb contents are sufficiently high to make significant contributions to the internal dose rate compared to the contribution from the K content. The U and Th contents are reduced, but not eliminated completely, by hydrofluoric (HF) acid etching.

Comparisons between the single-aliquot additive-dose (SAAD) and single-aliquot regenerative-dose (SAR) procedures are made using 150– 212 μm quartz grains separated from three sediment samples. Growth curves and equivalent doses from the two procedures are compared directly using single aliquots of quartz. With appropriate corrections for the loss of signals in our SAAD protocol, the SAAD and SAR growth curves coincide well. It is confirmed that the luminescence correction in the SAAD protocol can only be applied to samples for which the natural signal is in the linear part of the growth curve. A new correction method is proposed.

Based on the difference in the bleaching rate between IRSL and TL signals, a new method of assessing the bleaching of sedimentary feldspar is proposed. All measurements for De and the bleaching factor (normalized ratio of IRSL to TL) are carried out on the same grain. K-feldspar grains from two sediments, a marine and an alluvium, from Hong Kong were tested. Their bleaching factors indicate that bleaching of the marine sediment was not uniform, whereas the latter was relatively homogeneous. Furthermore, the relatively well-bleached grains in each sample were identified.

We have investigated the effects of annealing quartz at temperatures up to 1000°C on both the absolute sensitivity and on the growth curve shape, using quartz extracts from three sedimentary samples from widely separated locations. Growth curves up to 670 Gy were measured using the single-aliquot regenerative-dose protocol, which allows all heat treatments and OSL measurements to be performed on a single sub-sample, with a corresponding improvement in precision when compared with multiple-aliquot protocols. It is found that the degree of dose-dependent sensitivity change is dependent on the annealing temperature. Despite this, and absolute sensitivity changes of more than three orders of magnitude, the growth-curve shape is relatively independent of annealing temperature, especially at low doses.

A procedure of preheat/measurement, dose/preheat/measurement and preheat/measurement is proposed, in which all the measurements for the equivalent dose determination are made on a single aliquot of K-feldspar sample with the additive-dose method. Correction for the loss of IRSL signal due to preheat/measurement cycles is made using correction factors determined both at the beginning and the end of the measurement cycle. It is suggested that the optimal preheat condition for the sample can be determined by comparing the correction factors obtained from the two stages of analysis, as a function of preheat temperature. The most appropriate preheat for our K-feldspar sample is at 235°C for 10 min.

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 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.

An analysis method is introduced for traps which give rise to optically stimulated luminescence (OSL). For pulse-annealing experiments, the relationship between the temperature at which maximum OSL depletion occurs and the linear heating rate used to deplete the trapped charge is established, and this allows trap parameters to be determined. The lifetime at ambient temperature can be obtained from these parameters assuming first-order kinetics. Experimental data for a sedimentary K-feldspar separate are presented.

Equivalent dose determinations with IRSL and TL signals by the single disc regeneration method have been studied for a polymineral fine grain sample. The major problem is found to be the change in sensitivity for both signals; the sensitivity can either increase or decrease, depending on the dose and the heating profile applied. A method based on the IRSL signals to determine the range of equivalent dose with three sample discs was proposed.

Although infrared-stimulated luminescence (IRSL) signals in feldspars can be bleached rapidly by sunlight, there could still be a small amount of IRSL signal remaining in sediment grains if they have experienced only relatively short sunlight exposure before deposition. This remaining signal results in a “remnant dose” stored in the grain and is important for young samples but negligible for old samples. Several methods have been introduced to detect insufficient bleaching, and some of them can provide information on the extent of the bleaching. Others can only distinguish between samples bleached for a very long time and for a short time. Empirical methods are introduced to evaluate the possible values of equivalent dose accumulated since the grains were deposited. These methods involve the analysis of the equivalent doses and the natural IRSL signals obtained using single-disc dose determination methods.

Lifetime determinations for both IRSL and GLSL signals were carried out using a method of pulse annealing with different heating rates. For a sedimentary K-feldspar sample and ambient temperature of 10°C, lifetimes of 6.6 × 10 8 and 1.3 × 10 6 years were obtained for IRSL and GLSL signals respectively. The differences in thermal stability for IRSL and GLSL are supported by results from an isothermal annealing experiment. The difference in lifetime is interpreted by different groups of traps being sampled by both stimulation sources. The implications for optical dating limits are discussed.

Li, B., Li, S-H., Wintle, A. G., Zhao, H. (2010). Anomalous fading: A reply to the comment by Huntley on “Isochron measurements of naturally irradiated K-feldspar grains”. Radiation Measurements, 46(1), 164-165.