Stimulated Luminescence Signal Research Articles

New chronology of K-feldspar isochron optical dating (iIRSL) in the late Pleistocene coastal aeolian deposits of Southeast China

Old red sand (ORS), which developed during the late Pleistocene, is widely distributed along the coasts of the western Pacific and Indian Ocean. Recently, advancements in the Optically Stimulated Luminescence (OSL) dating technology have primarily determined its sedimentary age. However, in tropical and subtropical regions, chemical weathering can impact the calculation of environmental dose rates, potentially leading to age biases whose magnitude remains uncertain. The new K-feldspar isochron dating method (iIRSL) has the potential to address this issue. This approach effectively enhances the accuracy of age data by accounting for variations in past dose rates caused by chemical weathering and changes in water content during sample burial. This study used the iIRSL method to conduct infrared stimulated luminescence signal tests on ORS samples from the Haitan Island, south China. Five grain sizes of K-feldspar grains were extracted from each sample during experimentation. The single aliquot regenerative dose method (SAR) was utilized to determine the equivalent dose for each grain size and calculate age using the isochron method (iIRSL). Furthermore, it compared the iIRSL ages with quartz age (SAR). The results indicate that: (1) This study obtained four iIRSL ages, which are consistent with the ages obtained from quartz (SAR) within a reasonable range, ranging from 62.13 ± 4.85 to 39.44 ± 4.85 ka BP. (2) Comparison of the simulation results of different weathering degrees using the iIRSL method and K-feldspar two-step IRIR methods indicates that the iIRSL method can effectively mitigate the impact of chemical weathering on age determination, giving more reliable iIRSL ages. (3) The ORS along the southern coast of China mainly deposited during Marine Isotope Stages 5, 4, and 3, exhibiting relatively higher deposition rates during MIS 5 and MIS 3 at approximately 30 cm/ka and 15 cm/ka respectively. This suggests that the ORS was predominantly deposited during periods of elevated sea levels. However, it is important to note that the data from MIS 5 may have been influenced by the absence of samples from this particular stage and limitations in dating methods, resulting in a lower frequency-density of deposition ages during MIS 5 and creating an “illusion” of sediment interruption.

High-resolution luminescence-dated sediment record for the last two glacial-interglacial cycles from Rodderberg, Germany

The Rodderberg Volcanic Complex (RVC) is well-known for the long climate record archived in its crater basin, which lasts for several glacial-interglacial cycles. However, a detailed chronological framework is still lacking. Here, we perform high-resolution luminescence dating on a 72.8 m-long sediment core with the optically stimulated luminescence (OSL) signal from fine-grained (4–11 μm) quartz and three kinds of post-infrared infrared (pIRIR) stimulated luminescence signals from fine-grained polymineral fractions. Together with magnetic susceptibility, grain size and quartz OSL sensitivity measurements, a numerical age framework is built for the upper half of the sediment core. Quartz OSL ages align well with pIRIR ages for the last 45 ka, but they underestimate in relation to pIRIR ages for ages beyond 45 ka. The three pIRIR signals, including the pIRIR signal at 225 °C (pIRIR225), the pulsed pIRIR signal at 150 °C (pulsed pIRIR150) and the multi-elevated-temperature pIRIR at 250 °C (MET-pIRIR250), yield consistent ages up to ca. 250 ka at a sediment depth of 37.5 m. Below that depth, dating limits of the protocols are reached. Nevertheless, our results indicate that sediments below 37.5 m predate Marine Isotope Stage (MIS) 7. Altogether, obtained ages reveal continuous dust accumulation during MIS 7 and MIS 6. One erosional event happened at the end of the Eemian (MIS 5e), which eroded the Eemian soil. The sedimentation rate during the Weichselian glacial period is tenfold lower compared to the sedimentation rate observed during MIS 7–6. This low sedimentation rate likely arises from the cessation of slope wash effects and the occurrence of various wind erosional events alternating with dust deposition as the basin is filled by dust. A notably high sedimentation rate is observed at the transition from MIS 6 to the Eemian, marked by the deposition of a 7 m-thick loess layer between 135 and 129 (±5) ka. This high sedimentation rate could be attributed to intensified slope wash and solifluction processes resulting from the thawing of permafrost at the time of deglaciation. Alternatively, it might be a signature of Heinrich event 11, during which strong winds brought large amounts of dust into the basin within a short time.

Dose Rate Calibration of β Radiation Source in Risø TL/OSL-DA-20 Reader Device

This research is focused on determining the dose rate calibration of beta irradiation source in the Risø brand TL/OSL-DA-20 model thermoluminescence (TL) and optically stimulated luminescence (OSL) reader device manufactured by DTU Physics which is an integral component of the Technical University of Denmark (DTU). The beta radiation source of this device comprises a pellet-shaped Strontium ceramic made from the 90Sr/90Y radionuclide, with a half-life of approximately 29.1 years. This investigation provides a thorough examination of reproducing equivalent dose levels by comparing reproduced OSL signals with the OSL signals of calibration quartz crystals which were previously exposed to a 5 Gy beta radiation emission. Throughout this process, dose durations and equivalent dose levels were analysed on optically stimulated luminescence signals. The collected OSL data aims to ensure the precise calibration of the radioactive source, contributing to reliable results in dosimetric measurements. This calibrated device is utilized in the Luminescence Laboratory co-run by the Physics Department and Nuclear Materials Research and Application Center of Selçuk University. The determined dose rate of the beta radiation source is found as 0.065 Gy/second.

Insight into the dynamics of a long-runout mass movement using single-grain feldspar luminescence in the Pokhara Valley, Nepal

Abstract. Mass movements play an important role in landscape evolution of high mountain areas such as the Himalayas. Yet, establishing numerical age control and reconstructing transport dynamics of past events is challenging. To fill this research gap, we bring luminescence dating to the test in an extremely challenging environment: the Pokhara Valley in Nepal. This is challenging for two reasons: (i) the optically stimulated luminescence (OSL) sensitivity of quartz, typically the mineral of choice for dating sediments younger than 100 ka, is poor, and (ii) highly rapid and turbid conditions during mass movement transport hamper sufficient OSL signal resetting prior to deposition, which eventually results in age overestimation. Here, we first assess the applicability of single-grain feldspar dating of medieval mass movement deposits catastrophically emplaced in the Pokhara Valley. Second, we exploit the poor bleaching mechanisms to get insight into the sediment dynamics of this paleo-mass movement through bleaching proxies. The Pokhara Valley is a unique setting for our case study, considering the availability of an extensive independent radiocarbon dataset as a geochronological benchmark. Single-grain infrared stimulated luminescence (IRSL) signals were measured at 50 ∘C (IRSL-50) and post-infrared infrared stimulated luminescence signals at 150 ∘C (pIRIR-150). Our results show that the IRSL-50 signal is better bleached than the pIRIR-150 signal. A bootstrapped minimum age model (bMAM) is applied to retrieve the youngest subpopulation to estimate the paleodose. However, burial ages calculated with this paleodose overestimate the radiocarbon ages by an average factor of ∼23 (IRSL-50) and ∼72 (pIRIR-150), showing that dating of the Pokhara Formation with a single-grain approach was not successful for most samples. Some samples, however, only slightly overestimate the true emplacement age and thus could be used for a rough age estimation. Large inheritances in combination with the scatter in the single-grain dose distributions show that the sediments have been transported under extremely limited light exposure prior to deposition, which is consistent with the highly turbid nature of the sediment-laden flood and debris flows depositing the Pokhara gravels. To investigate the sediment transport dynamics in more detail, we studied three bleaching proxies: the percentage of grains in saturation 2D0 criteria, the percentage of best-bleached grains (2σ range of bMAM-De) and the overdispersion (OD). None of the three bleaching proxies indicate a spatial relationship with runout distance of the mass movement deposits. We interpret this as evidence for the lack of bleaching during transport, which reflects the catastrophic nature of the event. While not providing reliable burial ages of the Pokhara mass movement deposits, single-grain feldspar dating can potentially be used as an age range finder method. Our approach shows the potential of luminescence techniques to provide insights in sediment transport dynamics of extreme and rare mass movement events in mountainous regions.

Correlation between thermoluminescence and optically stimulated luminescence signal in BeO

Beryllium Oxide (BeO) is a promising dosimetric material that is rapidly becoming an essential instrument in Optically Stimulated Luminescence (OSL) dosimetry applications. Despite the potential of BeO as a luminescence dosimeter, gaps remain in understanding how its Thermoluminescence (TL) and Optically Stimulated Luminescence (OSL) signals are connected. Our study aimed at examining Residual Thermoluminescence (R-TL) glow curves after various bleaching times to find an association between TL traps and OSL components across a wide range of doses, at 40 mGy and from 10 to 100 Gy. OSL decay curves and intensities of R-TL glow curves were fitted to either pure exponential decay functions or to stretched exponential decay functions, due to optical attenuation, to determine the OSL components and the bleaching decay rates of each TL peak, respectively. A good correlation between the decay rates of the OSL components and bleaching decay rates of each TL peak for both high and low-dose irradiations was found only for the model functions considering optical attenuation in the material. Taken together, this qualitative method helped to identify various traps, and results revealed a more consistent luminescence mechanism between TL and OSL signals than was previously assumed. Further support for the correlation between TL and OSL was derived from thermal stability studies of the OSL signal and from the dose response of the TL peaks and the OSL signal after different thermal pretreatments. Different bleaching models were discussed to define the appropriate one for BeO. These results may enhance our understanding of BeO as a dosimeter.

The sensitisation of quartz extracted from andesite

Low quartz sensitivities have been reported in several studies in Iran, and in part this is presumed to be a result of the volcanic provenance of many of the sediments in the study areas. In this study we test experimentally whether a quartz sample, extracted from an andesitic rock and showing an insensitive fast component in the Optically Stimulated Luminescence (OSL) signal, can be sensitised using optical and thermal methods.The luminescence characteristics of quartz extracted from a rock sample from a landslide in Iran (Rudbar-Manjil) are compared to those of a well-characterised quartz sample. We find that very few of aliquots prepared from extracted quartz grains show any sensitivity of the most easily stimulated part of the OSL signal, but that ∼23% of aliquots give detectable initial signals after repeated dosing and bleaching. Surprisingly, a large fraction of the most easily stimulated quartz OSL is removed by infra-red stimulation, even though there is no significant IRSL signal in the UV. However thermal annealing at 700 °C gives rise to a test-dose response that is unaffected by IR. This annealing sensitises all aliquots to some degree and induces a signal which is stable up to 260 °C, in contrast to that following optical sensitisation, which begins to decrease when heated to 140 °C. The implications of these observations are discussed, both in terms of luminescence process and potential for dating.

Zeroing of IRSL signals in cobbles surfaces from a modern river floodplain in the Manas river, Tian Shan

A newly developing method, rock surface luminescence dating, provides a novel means of constraining the burial age of fluvial gravel and unveiling the transport and exposure-burial process of fluvial bed-load. A crucial requirement for successful age determination in luminescence dating of buried rock surfaces is that a sufficiently thick surficial layer was reset to a near-zero level of signal prior to deposition and burial. However, little such effort has been made on modern fluvial gravels from various depositional environments to provide a sound justification for the use of luminescence dating in such settings. In this study, we reported an investigation of daylight bleaching in modern cobbles with different sizes and shapes at a modern river floodplain from the Manas River, Tian Shan, to test the reliability and applicability of fluvial cobble optical dating. Four multi-elevated-temperature post-infrared infrared (MET-pIRIR) stimulated luminescence signals of rock slices were measured using a modified MET-pIRIR protocol to establish residual luminescence-depth profiles. The residual does of pIRIR and MET-pIRIR signals of sub-surface rock slices were also estimated using different modified SAR protocols. The results showed that the high temperature IRSL signal could be reset to ∼2–3 mm depth into cobbles surface and flat cobbles seem easier to bleach than spherical cobbles. The residual doses of sub-surface rock slices of cobbles from modern river floodplain was ∼0.4 Gy and ∼1.1 Gy for the IR50 and the pIRIR170 signal respectively, suggesting a residual age of ∼0.1 ka and ∼0.2 ka. The residual ages of MET-pIRIR signals of sub-surface rock slices of cobble MNS2-5 were ∼0.5–1 ka at higher stimulation temperature. Our results show that the fluvial cobble optical dating techniques have great potential for providing reliable chronologies for river floodplain gravel and other fluvial depositional events.

The effects of heat treatment on the OSL signal in sodium chloride crystals

Luminescence studies focusing on sodium chloride crystals have been conducted in various parts of the world, including Brazil, India, Greece, Türkiye, Australia, Spain, and Poland. This material shows great promise in the field of dosimetry, as it has demonstrated high sensitivity, excellent reproducibility, a linear response, and a low minimum detectable dose. Moreover, it holds significant potential for applications in accidental dosimetry, providing valuable results for dating and retrospective dosimetry purposes. Natural sodium chloride encompasses different types of salts, such as Himalayan black salt, pink salt, and sea salt. The presence of these salt variations is attributed to their composition, which includes not only pure sodium chloride but also other elements like magnesium, potassium, sulfur, and calcium. These additional elements contribute to the unique characteristics and properties exhibited by these types of salts. A comprehensive study was conducted to investigate the effects of thermal treatments on pink salt crystals, aiming to enhance their luminescent intensity and thereby improve their sensibility to detect ionizing radiation. By subjecting the crystals to various thermal treatments, we observed significant changes in their luminescent signals. Firstly, we observed a change in the shape of the Thermoluminescence (TL) curve, indicating modifications in the properties of the luminescent F-centers present in the crystals. Additionally, we noticed a significant increase in the Optically Stimulated Luminescence (OSL) signal, indicating a greater ability of the crystals to store and release energy under optical stimulation. A particularly interesting discovery was the reduction in intensity of the third component of the OSL signal in darker-toned crystals. Also the spontaneous regeneration reported by other researchers was almost eliminated. Furthermore, our results demonstrated only a 2.5% fluctuation in experimental repeatability, indicating high consistency and reliability of the obtained data.

Unlocking the effect of Li and Ce ions on the thermoluminescence and optically stimulated luminescence signals of the MgB4O7 compound.

Magnesium tetraborate (MgB4O7) is an example of a material that has attracted the attention of researchers in the field of ionising radiation dosimetry. Several challenges are present in order to achieve considerable advances in luminescence dosimetry. The incorporation of efficient dopants in the host matrix has been an experimentally useful but limited strategy. The lack of specific information about the introduced defects as well as their connection with the trapping and recombination processes associated with light emission may be quoted as challenging examples. Here, we demonstrate the influence of lithium incorporation on Optically Stimulated Luminescence (OSL)/Thermoluminescence (TL) signal modification/suppression of MgB4O7 by combining experimental and computational procedures. Li substitution into the Mg site leads to a signal suppression due to the probable quenching of the Fs and Fs+ centres in MgO and the formation of O''i, drastically reducing the possibility of MgO anti-Schottky defect formation in MgB4O7. When using Li-co-doped MgB4O7:Ce3+, the Li ions act as a charge balancer, facilitating the entry of Ce ions into the interstitial pores and making possible a positive synergistic effect on the luminescence and dosimetric properties. These findings provide new insights into designing more efficient dosimeters by tuning dopants.

Pulsed photoluminescence measurements using salt as a radiation accident dose detector material

To realize the retrospective measurement of public dose levels after a nuclear emergency, the optically stimulated luminescence radiation dose-response characteristics of salt were studied, and the relationship between the salt optically stimulated luminescence signal and ionizing radiation dose was determined. The effects of natural light, storage time, and preheating temperature on the salt optically stimulated luminescence signal were examined. The results show that salt as a photoluminescence dose measurement material has the advantages of convenient sampling, high throughput, short detection time, wide dose range, and low detection limit. The study lays the technical foundation for achieving the public dose assessment of salt pulse photoluminescence.

EFFECT OF DIFFERENT SOLVENTS ON THE OPTICALLY STIMULATED LUMINESCENCE SIGNAL FROM MGB4O7:CE,LI-LOADED POLYMER FILMS.

The detailed dose analysis at the extremities remains a challenge, without affecting operators' mobility and their tactile sense. Using films loaded with optically stimulated luminescence (OSL) crystals have been studied in order to overcome some of these challenges in 2D dosimetry. In this work, we investigated flexible polymeric films loaded with MgB4O7:Ce,Li to acquire a better understanding of the dependence of the dosimetric signal characteristics on the production process and the influence of using different powder grain sizes. In film production, five different solvents were used: acetone-benzene, dichloromethane, chloroform, tetrahydrofuran and formic acid. Our results indicate that acetone-benzene is the solvent mixture that less influences the signal emitted by treated crystals, in comparison with the signal emitted by the pristine crystal powder. Conversely, by using formic acid, the crystalline structure of the sample was most severely modified, leading to a drastic reduction of the emitted OSL signal. We found that the extent of the grain surface in contact with the solvent in the process is important and should be taken into consideration when choosing the proper grain size to be used. Highlights Polymeric films loaded with MgB4O7:Ce,Li crystals were produced using different solvents.Different effect on the OSL signal was found depending on the used solvent.Among the evaluated solvents, acetone-benzene was the one that less affected the OSL signal.

A simplified multiple aliquot regenerative dose protocol to extend the dating limit of K-feldspar pIRIR signal

The post-infrared infrared stimulated luminescence signal (pIRIR) from K-feldspar shows significantly less athermal fading than the conventional IRSL signal, thus it has been widely used for dating Quaternary deposits. With the single aliquot regenerative dose (SAR) protocol, the test dose signal is influenced by the preceding regenerative dose, and the characteristic saturation dose (D0) of the pIRIR signal is mostly in the range of 200–600 Gy, depending on the size of the test dose. According to the D0 value, the dating range of pIRIR is restricted to <300 ka with the SAR protocol. Here we present a multiple aliquot regenerative dose (MAR) protocol using low-temperature thermoluminescence (TL) signal for inter-aliquot normalisation. The multiple-elevated-temperature (MET) pIRIR signals up to 290 °C are investigated. The D0 increases to 850–1300 Gy with this protocol, which should represent the intrinsic D0 of IR or pIRIR signals of K-feldspar. Based on the higher D0, this protocol has the potential to date samples with equivalent doses (Des) up to 2000 Gy, i.e. up to ∼600 ka considering a dose rate of ∼3.5 Gy·ka−1. Applications of this MAR protocol on two loess samples from the Chinese Loess Plateau provide ages consistent with expected ages up to 350 ka, with the MET-pIRIR signal at 290 °C. However, tests on three fluvial and alluvial samples show age overestimation with the new MAR protocol as well as SAR protocol, which may result from the hard-to-bleach property of the high-temperature pIRIR signals. Simulations of fading correction indicate that the age will be over-corrected when the laboratory dose response curve has a D0 smaller than the true D0 of the signal. Caution should be taken in fading corrected ages measured with the conventional SAR protocol, as the D0 values are always underestimated in this case.

Thermally Transferred Optically Stimulated Luminescence, TT-OSL: a study on the responsible traps

Abstract Aim of this paper is to better investigate the Thermally Transferred Optically Stimulated Luminescence (TT-OSL) signal generated in quartz samples, both mineral quartz and quartz extracted from sediment, when they are heated after an optical bleaching. In recent years, TT-OSL has become an interesting dating technique because it can extend by an order of magnitude the age range over which OSL dating can be applied. We focused in particular on the source traps that generate this signal, studying the changes in TT-OSL due to the preheat temperature that induces the thermal transfer, and analysing the Thermoluminescence (TL) signals caused by OSL and TT-OSL measurements. By varying the preheating temperature, it was possible to identify the presence of a peak at ∼280-300°C, likely related to a trap responsible for the TT-OSL signal. A similar result was obtained by analysing the glow curves after an optical bleaching, which evidenced a peak at ∼270°C, comparable with a peak previously identified. It was also possible to highlight the fact that the OSL and TT-OSL signals are originated by different mechanisms due to the differences between the source traps responsible for them.

On the deconvolution of promptly measured luminescence signals in feldspars

Thermally and optically stimulated luminescence signals from feldspars have been the subject of numerous experimental and modeling studies, due to the importance of these signals in luminescence dosimetry and luminescence dating. Despite these extensive previous studies, there are no standardized computerized deconvolution methods for analyzing these signals in the literature. In this paper we present a simple and consistent method which can be used to perform computerized deconvolution of thermoluminescence (TL), continuous-wave infrared stimulated luminescence (CW-IRSL) and linearly-modulated (LM-IRSL) signals from feldspars. The method can be used with promptly measured luminescence signals from laboratory irradiated samples. R scripts are used in several examples to carry out the deconvolution of TL, CW-IRSL and LM-IRSL luminescence signals from different types of feldspars, including K feldspars extracted from bedrock and from a suite of geological museum samples. The results of the analysis show that the TL glow curves can be described in a uniform manner, as the superposition of several components corresponding to different activation energies. All TL, CW-IRSL and LM-IRSL signals can be described by a narrow range of the dimensionless acceptor density parameter, consistent with previous analysis of these luminescence signals in the literature, which have concluded that these luminescence signals are likely to share a common recombination center.

High-resolution palaeoenvironmental reconstruction at Zmajevac (Croatia) over the last three glacial/interglacial cycles

A high-resolution analysis of the Zmajevac loess-palaeosol sequence in East Croatia (Baranja) was performed with the purpose to get new insights into the palaeoenvironmental history during the last three glacial-interglacial cycles. The post-IR infrared stimulated luminescence signal of feldspar, stimulated at 290°C (thereafter pIRIR290) was used to establish a reliable chronological framework and revealed intensive sedimentation during (at least) the last 300 kyr, which was five times interrupted by climate optima resulting in the formation of soils (now palaeosols). The environmental magnetic measurements support the obtained luminescence chronology. Further chronological time control was reached by age modelling based on tie points from variations in frequency dependence of magnetic susceptibility and benthic δ18O variations from the LR04 stack of Lisiecki and Raymo (2005). The grain-size record provided information about the environmental conditions and dust accumulation. Additional palaeoenvironmental implications were provided by room temperature magnetic susceptibility and colourimetric analyses and revealed a continuously lower intensity of pedogenesis, coupled with constantly decreasing temperatures and precipitation from the oxygen isotope stage (OIS) 9 to the end of OIS 3. X-ray diffraction of the clay mineral fraction revealed chlorite, smectite and illitic material as dominant mineral phases. While clay minerals from loess are mostly detrital, smectite from palaeosols is partly of a pedogenic origin. The application of our multi-proxy approach, including relative and numerical dating techniques, provided new insights into a highly resolved terrestrial paleoenvironmental record of Eastern Croatia.

Modeling the charge deposition in quartz grains during natural irradiation and its influence on the optically stimulated luminescence signal

The rate of charge deposition in quartz grains irradiated in natural conditions is computed by radiation transport modeling. Quartz luminescence models are modified with the addition of the resulting charge deposition term, and the influence of this process on the optically stimulated luminescence (OSL) signal is analyzed. The results indicate that the charge deposition occurring in the quartz grain during the time of residence within rock could lead to the depletion of trapped holes in the recombination centres. For the two different quartz models investigated here, complete depletion is expected to occur for rock ages between 500 Ma and 1100 Ma. It is predicted that for sedimentary quartz derived from such rocks, the OSL signal is dominated by the slow component. It was also found that the shape and saturation level of the natural sensitivity-corrected dose response curve (DRC) of quartz is affected by the charge deposition; specifically, a linear reduction of the saturation level with the age of the rock is observed.

Comparison of Equivalent Doses Obtained with Various post-IR IRSL Dating Protocols of K-Feldspar

Abstract Five dating protocols with post-infrared infrared (IR) stimulated luminescence signals (i.e. pIRIR) were performed on the K-feldspar of loess samples. Two of them were the single-aliquot regenerative-dose protocol (SAR) with two-step pIRIR stimulation, with the first IR stimulation at 50°C or 200°C and the second at 290°C (pIR50IR290, pIR200IR290). Two of them were the SAR protocols with five-step or six-step IR stimulation at multiple elevated temperatures to 250°C or 300°C (MET-pIRIR250, MET-pIRIR300). The final one was the multiple-aliquot regenerative-dose (MAR) protocol with the MET-pIRIR300 signal, together with a 500°C heat treatment administered before the test dose (‘MAR with heat’). The results show that when the equivalent dose (D e) of the sample was less than 500 Gy, all of the protocols gave consistent results; however, when D e exceeded 750 Gy, all of the SAR protocols underestimated De . The pIR50IR290 signal had the highest degree of underestimation, while the pIR200IR290, MET-pIRIR250 and MET-pIRIR300 signals had similar De values and similar degrees of underestimation. Possible reasons for the SAR D e underestimation are discussed. We suggest that only the ‘MAR with heat’ protocol is suitable for samples with D e exceeding 750 Gy.

Characteristics of Pulsed Blue and Green Light Stimulated Luminescence Signals of Quartz and Feldspars

The post-infrared (post-IR) pulsed blue light stimulated luminescence (PBLSL) signal has been employed to determine the equivalent dose (D&lt;sub&gt;e&lt;/sub&gt;) of feldspar contaminated quartz grains, but it sometimes suffers from the interference of feldspars. Since the green light stimulated luminescence (GLSL) signal of feldspars might be more reduced by a prior IR stimulation, we compared the characteristics of post-IR PBLSL and post-IR pulsed GLSL (post-IR PGLSL) signals of quartz and feldspars in this study to evaluate the feasibility of employing the green light for pulsed stimulation. We investigated the effect of the signal integration period, pulsed stimulation temperature, and prior IR stimulation temperature on the intensities of post-IR PBLSL and post-IR PGLSL of quartz and feldspars, and evaluated the potential feldspar interference on these two signals for the hypothetical and artificial quartz-feldspar mixture. The results demonstrate a lower feldspars contribution for the post-IR PGLSL signal. The feldspar interference only slightly increases with the increase of integration period for the post-IR PGLSL signal measured at low stimulation temperature, which permits a long integration period to be employed to enhance the signal to noise ratio. This study shows that the green light is a promising alternative for pulsed stimulation to suppress the feldspar contribution.

Uniformity of Thermoluminescence and Optically Stimulated Luminescence Signals Over the Length of Doped LiMgPO4 Crystal Rods Grown by Micro-Pulling-Down Method.

The purpose of this work was to systematically assess the distribution of thermoluminescence (TL) and optically stimulated luminescence (OSL) properties along the length of crystals grown by the micro-pulling-down method, in relation to the microstructure and distribution of activators. We analyzed lithium magnesium phosphate (LiMgPO4; LMP) crystals doped with terbium (Tb; 0.8 mol%) or with a combination of thulium (Tm; 0.8 mol% or 1.2 mol%) and boron (B; 10 mol%). Crystals of several centimeters in length and 3 mm in diameter were cut into 20–40 slices, depending on length. For each sample, TL glow curves and OSL decay curves were examined. Optical microscopy and scanning electron microscopy were used to assess the microstructure and elemental composition of several selected samples. Two-dimensional TL readouts were performed to identify the areas with higher and lower signal emission. Our study showed that there may be significant differences not only in LMP sensitivity along the crystal’s axis but also on the surface of the slice. The distribution of activators varies depending on the type of crystals and strongly affects luminescence properties.

Optically Stimulated Luminescence Signal Resetting of Quartz Gouge During Subseismic to Seismic Frictional Sliding: A Case Study Using Granite‐Derived Quartz

AbstractAttempts to determine the age of faulting recorded by fault rocks have been made using K–Ar, fission‐track, electron spin resonance, and luminescence dating methods. Here we report the unambiguous reduction (resetting) of optically stimulated luminescence (OSL) signals of quartz gouge after friction experiments and estimate the seismological and geological conditions required for OSL signal resetting in natural fault zones. In the experiments, we used quartz sand with a particle size of &lt;150 μm and equivalent dose of 31.5 ± 16.6 Gy. Friction experiments were conducted with a rotary‐shear, high‐velocity friction apparatus at slip rates (V) of 200 μm s−1 to 1.3 m s−1, normal stress of 1.0 MPa, and displacement of 10 m. In the experiments conducted under dry conditions, the OSL signal starts to decrease from V = 0.25 m s−1 and becomes near zero at V ≥ 0.65 m s−1. OSL signal resetting is also observed in the experiment sheared at 1.3 m s−1 under water‐added conditions. At V = 0.25 and 0.40 m s−1, partial resetting occurs, which is characterized by coexistence of particles with and without an OSL signal. OSL signal intensity shows a strong correlation with applied power density and frictional heat during high‐velocity friction, and the signal exponentially decreases with increasing power density and temperature. The power density required for partial and complete OSL signal resetting is ~0.17 and 0.6 MW m−2, respectively. Assuming a co‐seismic fault slip rate of 0.6 m s−1, the depths required for partial and complete resetting are expected to be ≥11 and ≥42 m.