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.     

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.     

Optically stimulated luminescence (OSL) study of synthetic stishovite

Optically stimulated luminescence (OSL) of synthetic stishovite was investigated for a future dating technique of meteor impact craters. Luminescence around 330 nm was measured on the γ-ray irradiated stishovite under two stimulating light sources of infrared laser (830 nm) and blue light emitting diode set (470 nm). Thermoluminescence (TL) studies before and after the OSL measurements showed the intensities around 100–200°C and 220–350°C to increase and those around 350–450°C to decrease. This indicates that a part of deep-trapped charges excited during the OSL measurements were retrapped by shallower traps. The infrared stimulated luminescence (IRSL) after the TL measurement up to 450°C could not be detected, while the blue light stimulated luminescence (BLSL) after TL had about one-tenth of the intensity before TL. This indicates that a part of the charges in shallower traps were detrapped thermally and returned to the deeper traps which were related to BLSL. The result implies that some of the BLSL-related traps are quite stable at room temperature and could be used for geological dating. In addition, two paramagnetic centers produced by sudden release of high pressure in synthesis process were found in the unirradiated stishovite by electron spin resonance (ESR). Their g-factors are g=2.00181 and g=2.00062 for an axial signal and g=2.00305 for the other isotropic signal. These signals could be used for an evidence of impacts if those signals could be stored in geological time.     

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.     

Dating bricks of the last two millennia from Newcastle upon Tyne: a preliminary study

Bricks from a group of four independently dated late medieval buildings in Newcastle upon Tyne have been tested to establish their suitability for luminescence dating as part of a wider study of the dating of post-Roman and medieval brick buildings. The luminescence characteristics of quartz extracted from the bricks were determined using TL (210°C peak) and OSL measurement procedures. Both TL and OSL measurement procedures based on SAR and SARA protocols were applied to determine the palaeodose. The luminescence dates for three sampled locations are in good agreement with the assigned architectural dates; the fourth appears to be older raising doubts concerning the architectural assessment of the sampled phase.     

Luminescence dating: laboratory procedures and protocols

In the last 30 years, from 1967 to 1997, the use of luminescence signals from naturally occurring minerals has gone though a major metamorphosis, from thermoluminescence (TL) dating of pottery to optically stimulated luminescence (OSL) dating of sediments. Laboratory procedures for dating sediments have been adapted from those for pottery and new procedures have been developed as the need arises.

The majority of sediment dating applications are carried out on quartz and potassium-rich feldspars and the general characteristics of the TL and OSL signals from these minerals are reviewed. For sediments some new problems were encountered, with some grains perhaps not being completely bleached at deposition. For OSL signals there is no simple procedure for the selection of a thermally stable signal, as there had been in the case of pottery.

Many different laboratory protocols have been developed as our understanding of the fundamental behaviour of luminescence signals from quartz and feldspar has improved. These protocols are explained and discussed, giving the advantages and disadvantages of each procedure as applied to different types of sediment.

This review is presented as a guide to the selection of the most appropriate procedure for a particular dating application.     

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.     

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.     

Luminescence properties of biotite relevant to dating and dosimetry

Biotite mineral grains from granitic rocks were subjected to luminescence studies with optical and thermal stimulation. Moderate thermoluminescence (TL) signals and weak optically stimulated luminescence (OSL) with blue-green light stimulation were detected after 50 Gy beta irradiation. No detectable infrared-stimulated luminescence (IRSL) was observed for natural and laboratory beta-irradiated samples. TL peaks at 118, 300, 360 and 480 °C can be identified from laboratory-irradiated samples. The 360 °C TL peak saturates at a higher dose than quartz, but shows significant anomalous fading after 80 days stored at room temperature. The potentials and problems for biotite used as a natural dosimeter are 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.     

Comparison of the properties of various optically stimulated luminescence signals from potassium feldspar

Various optically stimulated luminescence signals from K-feldspar have been used to determine the equivalent doses of sediment samples. Understanding the properties of these optical signals is critical to evaluate their applicability and limitations to optical dating. In this paper, some properties of IRSL, post-IR OSL and post-IR IRSL signals (detected in the UV region using U-340 filters) from a museum sample of K-feldspar were investigated by analyzing the relationships between optical and TL signals, and the effect of optical bleaching and heating on optical signals. The trap parameters of the different optical signals were calculated using the pulse annealing method. The results show that this sample exhibits two regenerated TL peaks at ～140 and ～330 °C. Corresponding to the low temperature TL peak, the OSL and post-IR OSL signals appear to be more associated with lower temperature TL than the IRSL signal measured at 50 °C. Corresponding to the high temperature TL peak, the post-IR IRSL signals mainly originate from the more thermally stable traps associated with the high temperature TL, compared with the IRSL and post-IR OSL signals. However, the post-IR IRSL_225 °C signal is shown to be hard to be bleached by blue light and simulated sunlight, compared with the IRSL_50 °C and low temperature post-IR IRSL signals. The implication for optical dating is that the elevated temperature post-IR IRSL signals can be preferentially applied over other signals from K-feldspar, but it is desirable that the effectiveness of the pre-depositional zeroing of these signals is assessed.     

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.     

Luminescence spectra of alkalifeldspars and plagioclases

Feldspars are widely used as dosimeters in dating archaeological and geological materials by thermally or optically stimulated luminescence (TL, OSL). The TL, (IR)OSL and phosphorescence (following gamma irradiation) spectra of 26 samples covering the orthoclase-albite-anorthite ternary system, which were characterized by microscopy and X-ray diffraction analysis, were measured using the Freiberg high sensitive luminescence spectrometer. The range of observation for TL (up to 350°C) and phosphorescence was (200–800) nm. IR (880 nm) stimulated luminescence light has been detected between 330 nm and 660 nm. Representative examples of our systematic investigations on the luminescence behaviour of alkalifeldspars and plagioclases are presented.     

Improving the TT-OSL SAR protocol through source trap characterisation

Thermally-transferred optically stimulated luminescence (TT-OSL) extends the age range of OSL dating using quartz. A set of experiments have been undertaken to determine the kinetic parameters of the TT-OSL source traps, and this information has been used to propose an improved TT-OSL single aliquot regenerative (SAR) dose protocol. By combining together OSL and thermoluminescence (TL) measurements on fine-grained quartz, a correspondence between TL peaks and the TT-OSL signal is found. The thermal stability of the main TT-OSL trap was estimated by applying Hoogenstraaten’s method and allowing for thermal quenching; this predicts a lifetime of 4.5 Ma at 10 °C. A set of experiments were undertaken to refine the treatment needed at the end of each SAR cycle to erase the previously acquired TT-OSL signal. An improved TT-OSL SAR protocol using this treatment is proposed, and it is tested on quartz from a young Holocene sample. These tests yielded excellent recycling ratios and excellent dose recovery.     

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.     

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.     

On the pre-dose sensitization of the various components of the LM-OSL signal of annealed quartz; comparison with the case of 110 °C TL peak

Pre-dose sensitization of various components of LM-OSL signal of a Nigerian annealed quartz sample has been investigated along side with that of 110 °C TL peak in this work. Successive cycles of irradiations and TL/OSL readings using different heating rates were employed to attain pre-dose sensitization. The results showed that the pre-dose sensitization factor of 110 °C TL peak depends strongly on the heating rate of thermal activation. The pre-dose sensitization of 110 °C TL and all components of RT LM-OSL yield HR dependence on the sensitization after TA. This dependence was ascribed to the different heating time associated with each HR. Sensitization of LM-OSL measured at 125 °C generally does not show dependence on HR of TA. This was with the exception of components C₁ and C₃. Increasing sensitization pattern with increasing HR suggests a correlation between the TL glow-peak at 110 °C, the component C₄ of RT LM-OSL and the component C₃ of the LM-OSL signal at 125 °C. Extension of the present investigation to diverse quartz kinds from different origins was suggested in order to study the prevalence of the pre-dose sensitization on component C₄ of RT LM-OSL. Finally fast heating is suggested for lower sensitization of fast component while applying OSL dating protocols.     

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.     

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.     

Luminescence property of volcanic quartz and the use of red isothermal TL for dating tephras

An optically stimulated luminescence (OSL) age obtained from a Japanese tephra using quartz phenocrysts severely underestimated the known age. The characteristics of the OSL signals were investigated in order to understand the cause of the underestimation; the main OSL component of volcanic quartz has a thermodynamic lifetime of about 1700 years at room temperature, and it also seems to fade anomalously (i.e. athermally). Measurement of conventional red thermoluminescence (RTL) using a Ga–As photomultiplier tube was difficult due to the presence of a strong thermal background, although RTL gave an age consistent with the independent age. Furthermore, red isothermal TL (RITL) at 380 °C allowed the RTL signal to be separated from to the thermal background, and RITL ages of three volcanic quartz samples show good agreement with independent ages.