A luminescence dating intercomparison based on a Danish beach-ridge sand

There is a need for large scale intercomparisons to determine the degree of coherence of luminescence dating measurements made by different laboratories. Here we describe results from a laboratory intercomparison sample based on a quartz-rich aeolian and/or coastal marine sand ridge from the Skagen peninsula, northern Jutland (Denmark). About 200 kg of sand was sampled at night from a single beach ridge. The sand was homogenised using a cement mixer and packed in ∼700 moisture and light-tight bags for distribution. The quartz luminescence characteristics are satisfactory (e.g. fast-component dominated and good dose recovery) and our own equivalent dose determinations and measurements of radionuclide concentrations for twenty of these bags demonstrate the degree of homogenisation. One natural sample and one sample of pre-processed quartz was made available on request; analysis of all the responses gives a mean dose (pre-processed quartz) of 4.58 Gy, σ = 0.40 (n = 26), to be compared to the mean dose (self-extracted quartz) of 4.52 Gy, σ = 0.55 (n = 21). The mean age is 3.99 ± 0.14 ka, σ = 0.71 (n = 22), i.e. a relative standard deviation of 18%. We present an analysis of all the important quantitative and qualitative responses we received between 2007 and 2012 and discuss the implications for our dating community and for users of luminescence ages.     

Red luminescence from potassium feldspar for dating applications: a study of some properties relevant for dating

Aspects of the red thermoluminescence (RTL) and IR (833±5 nm) stimulated red (λ_emission=600–750 nm) luminescence (orange-red IRSL) of potassium feldspar from different origins are described. Anomalous fading of RTL (300–500°C) from a selection of potassium feldspar samples was tested. High temperature RTL (300–450°C) exhibits less anomalous fading in comparison to UV luminescence, for the samples under study. The result supports the contention of Zink and Visocekas (1997) that the red TL emission from feldspar does not fade. It was found that RTL is bleachable due to IR exposure, and the relationship between RTL lost and orange-red IRSL produced is linear. It is shown that around one third of the trapped charge responsible for the orange-red IRSL signal gives rise to an RTL signal, indicating that some traps and luminescence centres are shared for RTL and orange-red IRSL.

Specific characteristics of orange-red IRSL from feldspar were identified. It was found that the orange-red IRSL decay curve is bleachable by IR and daylight and can be described by the sum of three exponential components. Orange-red IRSL fading was tested. Short-term storage tests (up to 2 weeks) showed no fading. Longer-term (ca. months) storage of orange-red IRSL do in fact indicate fading, though at levels considerably lower than for the UV emission. The contradictory result is possibly due to the detection wavelength. As such, it is highly likely that the long-term fading experiment is strongly influenced by the feldspar emission centred at ca. 570 nm, which exhibits anomalous fading, while the short-term fading experiment is more greatly influenced by the far red emission centred at ca. 710 nm that in comparison to UV emission shows no or less fading.     

The fast ratio: A rapid measure for testing the dominance of the fast component in the initial OSL signal from quartz

The signal from the fast component is usually considered preferable for quartz optically stimulated luminescence (OSL) dating, however its presence in a continuous wave (CW) OSL signal is often assumed, rather than verified. This paper presents an objective measure (termed the fast ratio) for testing the dominance of the fast component in the initial part of a quartz OSL signal. The ratio is based upon the photo ionisation cross-sections of the fast and medium components and the power of the measurement equipment used to record the OSL signal, and it compares parts of the OSL signal selected to represent the fast and medium components. The ability of the fast ratio to distinguish between samples whose CW-OSL signal is dominated by the fast and non-fast components is demonstrated by comparing the fast ratio with the contribution of the fast component calculated from curve deconvolution of measured OSL signals and from simulated data. The ratio offers a rapid method for screening a large number of OSL signals obtained for individual equivalent dose estimates, it can be calculated and applied as easily as other routine screening methods, and is transferrable between different aliquots, samples and measurement equipment.     

Optically stimulated luminescence dating properties of Martian sediment analogue materials exposed to a simulated Martian solar spectral environment

Deciphering the geomorphic, climatic, and hydrologic history of Mars will require an extensive geochronology on numerous time scales from both returned samples and in-situ measurements. Optically stimulated luminescence dating (OSL), or optical dating, is an established terrestrial geochronological method that is being developed as a member of a suite of dating tools for Mars. As part of this development process, we have built an optical system simulating the calculated Martian solar spectral irradiance taking into account seasonal variations due to attenuation of dust and the planet's orbital position and used it to catalogue the UV dosimetric response and optical dating behavior of a group of sediment analogues exposed to a simulated Martian spectral environment (SMSE) for the surface of the planet. Our results suggest that optical dating should not be compromised by the interaction of the enhanced UV radiation in the Martian spectrum with K-feldspar, Ca-feldspar, anhydrite, or hydrous Ca and Mg sulfates on Mars. However, Na-feldspar appears to be capable of acquiring and retaining an OSL signal under SMSE conditions, which could present a challenge for optical dating on Mars in sedimentary deposits containing more than a trace quantity of sodic feldspars.     

Optically stimulated luminescence dating of Holocene alluvial fans,East Anatolian Fault System,Turkey

In this study, the optically stimulated luminescence dating technique was used to determine the time of deposition of alluvial sediment samples from the Türko?lu-Antakya segment of the East Anatolian Fault System (EAFS) in Turkey. The double-single aliquot regenerative dose protocol on fine grain samples was used to estimate equivalent doses (D_e). Annual dose rate was computed using elemental concentration of uranium (U) and thorium (Th) determined by using thick-source alpha counting and potassium (K) concentrations using X-ray fluorescence and/or atomic absorption spectroscopy. The environmental dose was measured in situ using α-Al₂O₃:C chips inside plastic tubes for a year. The two different bulk sediment samples collected from the Islahiye trench yielded ages of 4.54?±?0.28 and 2.91?±?0.23?ka. We also obtained a 2.60?±?0.18?ka age for the alluvial deposit in the K?ranyurdu trench and 2.31?±?0.14?ka age for an excavation area called Malzeme Oca??. These ages were consistent with the corresponding calibrated Carbon-14 (¹⁴C) ages of the region. The differences between the determined ages were insufficient to clearly distinguish the disturbance event from the effects of bioturbation, biological mixing, or other sources of D_e variation in the region. They provide a record of alluvial aggradation in the region and may determine undocumented historical earthquake events.     

Portable gamma spectrometry with cerium-doped lanthanum bromide scintillators: Suitability assessments for luminescence and electron spin resonance dating applications

Cerium-doped lanthanum bromide (LaBr₃:Ce) crystals offer a range of improved scintillation properties over traditional NaI:Tl crystals for in situ gamma spectrometry. At present, however, it remains unclear whether the internal radioactivity of LaBr₃:Ce detectors compromises their suitability for low-level activity radioisotope measurements of natural sedimentary deposits, such as those required in luminescence and electron spin resonance (ESR) dating. In this study we investigate the suitability of a commercial LaBr₃:Ce detector for measuring individual concentrations of ⁴⁰K, ²³⁸U and ²³²Th using predefined ‘energy windows’ from gamma ray spectra. Performance tests have been undertaken using reference materials with well-constrained radioisotope concentrations (the Oxford calibration blocks) and compared with results obtained for a NaI:Tl detector of the same geometry. These tests reveal that the LaBr₃:Ce detector has a non-negligible intrinsic activity that needs to be accurately quantified prior to measuring any gamma ray spectra in the field. Compared to the NaI:Tl detector, the energy resolution of the LaBr₃:Ce detector is improved by a factor of two, or more, for the main indicator isotope photopeaks in the ⁴⁰K, ²³⁸U and ²³²Th decay series. Signal-to-noise ratios for the LaBr₃:Ce detector show a 25-35% improvement over those of the NaI:Tl detector. In addition, the LaBr₃:Ce detector is characterised by suitable energy linearity over the full spectral range of interest for the ⁴⁰K, ²³⁸U and ²³²Th decay series. Replicate gamma ray measurements made with the LaBr₃:Ce and NaI:Tl detectors for 20 natural sedimentary samples from the Lower Tejo River basin, Portugal, and the Duero River basin, Spain, yield consistent radioisotope concentrations and gamma dose rate estimates. These results are encouraging and suggest that LaBr₃:Ce detectors can provide suitable estimates of individual radioisotope concentrations in low-level activity (0.5-1.5 Gy/ka) environments, providing that their intrinsic activity is adequately measured and subtracted from field spectra. Our comparison also reveals that subtraction of the intrinsic activity from LaBr₃:Ce spectra produces a significant reduction in the precision with which radionuclide concentrations can be determined using the ‘energy windows’ approach. This shortcoming necessitates longer counting times in natural sedimentary environments and overshadows the practical advantages that LaBr₃:Ce detectors might otherwise offer for luminescence and ESR dating applications.     

Quartz luminescence response to a mixed alpha-beta field: Investigations on Romanian loess

Previous SAR-OSL dating studies using quartz extracted from Romanian and Serbian loess samples report SAR-OSL dose–response curves on fine grained (4–11 μm) quartz that grow to much higher doses compared to those of coarse-grained (63–90, 90–125, 125–180 μm) quartz. Furthermore, quartz SAR-OSL laboratory dose response curves do not reflect the growth of the OSL signal in nature. A main difference in coarse- and fine-grained quartz dating lies in the alpha irradiation history, but the effect of mixed alpha-beta fields has so far received little attention. In the present study we investigate whether the alpha dose experienced by fine grains over geological cycles of irradiation and bleaching may have an effect on the saturation characteristics of the laboratory dose response. By applying time resolved optically stimulated luminescence we confirm that the OSL signals induced in quartz by alpha and beta radiation follow the same recombination path. We also show that a mixed alpha-beta dose response reproduces the beta dose response only up to about 800 Gy. Assuming an a-value of 0.04 we have shown that laboratory alpha and beta dose response curves overlap up to effective alpha doses of ∼50 Gy. Based on these results, we conclude that exposure of fine grains to alpha radiation during burial and transport cycles prior to deposition, as well exposure to the mixed radiation field experienced during burial are not responsible for the age discrepancies previously reported on fine and coarse grained quartz extracted from Romanian and Serbian loess.     

Sediment dating by luminescence: a review

In the present article we review applications of luminescence methods for the determination of the age of sediments for Quaternary Earth science. “Sediment” is taken to include any mineral particles transported by wind, water and/or ice and subsequently deposited. Methodology is not discussed per se but appears in context. The emphasis is on recent work and is illustrative rather than exhaustive. Applications in archaeology are mentioned only briefly. Successful dating requires that the luminescence signal has been zeroed by sunlight at the time the sediment was laid down. Dune sands and loess transported in full daylight usually satisfy this condition and have been dated by both traditional thermoluminescence and by optical methods. Optical dating is advantageous for less well-bleached sediments, such as are found in colder climates and those laid down by fluvial and glacial processes, although the prospects for dating the latter are shown to be poor. Among less common contexts are volcanic eruptions, earthquake faults and tsunami deposits. The dating of very young sediments, less than 2 ka, is demonstrated and the factors limiting the dating of very old sediments, 500 ka to 1 Ma, are discussed. Validation of any dating method by comparison with other methods is necessary; luminescence ages have been successfully compared with ages obtained by, for example, ¹⁴C, U–Th series and δ¹⁸O isotope ratios. The most difficult problems encountered in dating quartz, feldspars and undifferentiated fine grain mixtures include: anomalous fading (which leads to underestimates of age), incomplete zeroing (which gives overestimates) and sample inhomogeneity. Methods devised to minimise these effects include preheating regimes, selection of observing wavelengths and of stimulating wavelengths for optical dating, the use of single aliquot and single grain measurements. The use of appropriate data analysis procedures is also important. Advice on current best practice on procedures for obtaining reliable ages is offered and, in all applications, there are suggestions as to where further research might be directed.     

A survey of the signal stability and radiation dose response of sulfates in the context of adapting optical dating for Mars

The Martian landscape is currently dominated by eolian processes, and eolian dunes are a direct geomorphic expression of the dynamic interaction between the atmosphere and the lithosphere of planets. The timing, frequency, and spatial extent of dune mobility directly reflects changing climatic conditions, therefore, sedimentary depositional ages are important for understanding the paleoclimatic and geomorphologic history of features and processes present on the surface of the Earth or Mars. Optical dating is an established terrestrial dosimetric dating technique that is being developed for this task on Mars. Gypsum and anhydrite are two of the most stable and abundant sulfate species found on the Earth, and they have been discovered in Martian sediments along with various magnesium sulfates and jarosite. In this study, the optical dating properties of various Ca-, Mg-, and Fe-bearing sulfates were documented to help evaluate the influence they may have on in-situ optical dating in eolian environments on Mars. Single-aliquot regenerative-dose (SAR) experimental procedures have been adapted to characterize the radiation dose response and signal stability of the Martian sulfate analogs. Jarosite was dosimetrically inert in our experiments. The radiation dose response of the Ca- and Mg-sulfates was monotonically increasing in all cases with characteristic doses ranging from ∼100 to ∼1000 Gy. Short-term signal fading also varied considerably in the Ca- and Mg-sulfates ranging from ∼0% to ∼40% per decade for these materials. These results suggest that the OSL properties of Ca- and Mg-sulfates will need to be considered when developing protocols for in-situ optical dating on Mars, but more enticingly, our results foreshadow the potential for gypsum to be developed as a geochronometer for Mars or the Earth.     

A new mathematical approximation of sunlight attenuation in rocks for surface luminescence dating

The attenuation of sunlight through different rock surfaces and the thermoluminescence (TL) or Optical stimulated luminescence (OSL) residuals clock resetting derived from sunlight induced eviction of electrons from electron traps, is a prerequisite criterion for potential dating. The modeling of change of residual luminescence as a function of two variables, the solar radiation path length (or depth) and exposure time offers further insight into the dating concept. The double exponential function modeling based on the Lambert-Beer law, valid under certain assumptions, constructed by a quasi-manual equation fails to offer a general and statistically sound expression of the best fit for most rock types. A cumulative log-normal distribution fitting provides a most satisfactory mathematical approximation for marbles, marble schists and granites, where absorption coefficient and residual luminescence parameters are defined per each type of rock or marble quarry. The new model is applied on available data and age determination tests.     

Assessing the impact of IR stimulation at increasing temperatures to the OSL signal of contaminated quartz

The purpose of the present study is to identify the effect of the increasing temperature IR stimulation to the component-resolved OSL luminescence signal of mixed quartz-feldspars material. Post IR OSL signals measured at 110 °C were analysed via only general order kinetic terms, while IR signals obtained at increasing temperatures were de-convolved using the sum of general order kinetics plus a tunnelling component. By increasing stimulation temperature, it was demonstrated that IRSL at temperatures above 50 °C does not only stimulate feldspar but also stimulates both fast and medium quartz OSL components. In the temperature range between 175 and 250 °C, the IRSL initial intensity is dominated by the fast OSL component. Estimated equivalent doses using either Post-IR₁₇₅.OSL₁₁₀ as well as IRSL₁₇₅ (with the indices indicating the measurement temperature) are in good agreement between each other, due to both stimulating quartz. Finally, the physical meaningfulness of the fitting parameters for the tunnelling component is also discussed.     

Measuring modulated luminescence using non-modulated stimulation: ramping the sample period

Conventional methods of recording linearly modulated (LM) optically stimulated luminescence (OSL) require control over either the exciting light intensity, or the ability to pulse the source. For many light sources (e.g. constant-power CW lasers, arc lamps and synchrotrons) this can be problematic. Directly analogous results to LM-OSL can, however, be achieved with non-modulated excitation sources, by ramping the sample period (RSP) of luminescence detection. RSP-OSL has the distinct advantage over LM-OSL in that, since the excitation remains at full power, data accumulation times (that can be considerable) can be reduced by typically 50%. RSP methods are universally applicable and can be employed, for example, where the excitation source is constant heat, rather than light: here, iso-thermal decay of phosphorescence becomes recorded as a sequence of peaks, corresponding to de-trapping of charge from different defect levels, and is particularly useful for analysing shallow-trap effects. RSP methods are also useful in providing significant compaction of data sets, where signal analysis is required of overlapping systems having a wide range of decay kinetics.     

Simulations of fast component and slow component of SMBI on HL-2A tokamak

It is very important to improve the penetration depth and fueling efficiency of supersonic molecular beam injection(SMBI) especially for the next generation fusion devices such as ITER. Two components, a fast component(FC) and a slow component(SC), have been observed in the HL-2A SMBI experiments for several years, and the FC can penetrate much more deeply than the common SMBIs which draws a great deal of attention for a better fueling method. It is the first time to the FC and SC of SMBI have been simulated and interpreted in theory and simulation in this paper with the trans-neut module of the BOUT++ code. The simulation results of the FC and SC are clear and distinguishable in the same way as the observation in experiment. For the major mechanism of the FC and SC, it is found that although the difference in the injection velocity has some effect on the penetration depth difference between the FC and SC, it is mainly caused by the self-blocking effect of the first ionized SMB. We also discuss the influence of the initial plasma density on the FC and SC,and the variation of the SC penetration depth with its injection velocity.     

The problem of dating quartz 2: Synchrotron generated X-ray excited optical luminescence (XEOL) from quartz

The luminescence emission of quartz is used in optically stimulated luminescence dating (OSL), however the precise origins of the emission are unclear. A suite of quartz samples were analysed using X-ray excited optical luminescence (XEOL). Radiation dose effects were observed whereby the UV emissions (3.8 and 3.4 eV) were depleted to the benefit of the red emission (1.9–2.0 eV). Samples were excited at ∼7 keV. Understanding why some quartz emit light more brightly than others will increase the efficiency and precision of OSL analyses.     

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     

Impact of selective excitation on carbon longitudinal relaxation: Towards fast solid-state NMR techniques

The effect of selective pulses on the apparent carbon longitudinal relaxation is investigated in three fully ¹³C-labeled systems, histidine as a model system and two proteins MerP and YajG. It is shown that the longitudinal relaxation of a selectively excited carbon spin is greatly enhanced, mainly because of fast spin-diffusion. This relaxation enhancement allows reducing the time necessary for polarization recovery between two experiments. This effect can be exploited either to improve the sensitivity of NMR experiments or to reduce the experimental time. Using selective carbon excitation combined with fast pulsing on fully ¹³C-labeled proteins, a sensitivity improvement of 20–45% over standard cross-polarization methods is predicted from the measured relaxation times.     

Spectral information from minerals relevant for luminescence dating

The paper reviews basic spectral features of luminescence from minerals used in dating and allied research. Luminescence production is a result of multiple interactions within the imperfect crystal lattice and spectral information is not limited to the emission of light. Results of spectral investigations of luminescence emission during thermal stimulation (TL) or optical stimulation (OSL) form the main part of the paper. However, information on luminescence excitation and light absorption spectroscopy is also presented and possible links between luminescence production in minerals and particular lattice defects are considered. Quartz and feldspars, the most commonly used minerals, receive special attention, but the review includes other materials such as polymineral fine-grained fractions from sediments, zircon, calcite and other salts (halite, sulfate), meteorites, flint, volcanic materials (obsidian, tephra), ceramics and metallurgical slags. Although a wide range of different luminescence emission wavebands occur, it can be shown that certain emissions dominate in particular materials. Basic dosimetric properties are often known just for single emission wavebands of a particular mineral, and are listed in this case. The paper also aims to provide a starting point and inspiration for the study of other TL and OSL emissions, with particular regard to their potential and suitability for dating and related dosimetry tasks. These investigations, involving palaeodose determination based on an emission waveband with known characteristics, need careful separation of the particular emission peak, which may be influenced by its behaviour during the dating procedure (sample preparation, irradiation, preheat treatments, luminescence measurements, etc.). Spectral information available in this context and some technical remarks on the experimental conditions will be given to pave the way for conventional TL or OSL measurements in luminescence dating and dosimetry using natural or semi-natural materials.     

A fast infrared radiative transfer model based on the adding-doubling method for hyperspectral remote-sensing applications

A fast infrared radiative transfer (RT) model is developed on the basis of the adding-doubling principle, hereafter referred to as FIRTM-AD, to facilitate the forward RT simulations involved in hyperspectral remote-sensing applications under cloudy-sky conditions. A pre-computed look-up table (LUT) of the bidirectional reflection and transmission functions and emissivities of ice clouds in conjunction with efficient interpolation schemes is used in FIRTM-AD to alleviate the computational burden of the doubling process. FIRTM-AD is applicable to a variety of cloud conditions, including vertically inhomogeneous or multilayered clouds. In particular, this RT model is suitable for the computation of high-spectral-resolution radiance and brightness temperature (BT) spectra at both the top-of-atmosphere and surface, and thus is useful for satellite and ground-based hyperspectral sensors. In terms of computer CPU time, FIRTM-AD is approximately 100-250 times faster than the well-known discrete-ordinate (DISORT) RT model for the same conditions. The errors of FIRTM-AD, specified as root-mean-square (RMS) BT differences with respect to their DISORT counterparts, are generally smaller than 0.1 K.     

The potential of luminescence signals from electronic components for accident dosimetry

This study investigated the optically stimulated luminescence of a large number of electronic components extracted from both old and new generation mobile phones and chip modules of phone cards. Most resistors and all chip modules studied present a linear dose response (R > 0.99) in the dose range investigated (200 mGy up to 6 Gy, respectively 10 Gy), while capacitors, inductors and integrated circuits generally have a non-linear growth (exponential or cubic). For our experimental setup, an average specific luminescence of ∼20,000 cts in 2 s/Gy (n = 10) and ∼6000 cts in 2 s/Gy (n = 14) was obtained for two types of chip modules with a relatively high degree of homogeneity (relative standard deviation of 23% and 31%) and a minimum detectable dose of 7 mGy for immediate measurement. The investigated signals show small sensitivity changes (generally <10%) after repeated cycles of irradiation and readout. Preliminary fading measurements are presented. It can be concluded that most mobile phones and phone card components have a significant potential as retrospective luminescence dosimeters.