To browse Academia. Skip to main content. Log In Sign Up. Luminescence dating: basics, methods and applications Quaternary , Daniel Richter.
For suitable curve fitting, construction of the latter requires at least three different regenerative dose points plus a zero dose point. Flexibility in the SAR protocol permits an increase in the number of dose Fig.
Tx is the luminescence response to a constant test The performance of each individual SAR cycle dose e. The first test considers the signal Abb. Values above zero indicate that an punkte z. Tx ist das Lumineszenzsignal, unwanted signal was induced by preheating das aus der Bestrahlung mit einer konstanten Testdo- the sample prior to measurement recupera- sis z.
The second test ability of the measurement procedure. If these recycling ratio confirms whether correction tests do not provide acceptable results it is nec- for sensitivity change was successful. This test essary to modify the measurement procedure. If the sensitivity correction was of minerals are different in different geological successful, the ratio of the two measurements settings.
Hence, it is mandatory to carry out a will be unity. The lowest regenerative dose is measured twice, at the beginning and end of each individual SAR cycle, to ensure that sensitivity changes have been sufficiently corrected for. The phenomenon the natural dose in the SAR protocol and the is similar to the effect of recuperation cf. A simple test to the best achievable precision.
This very much identify if thermal transfer affects a sample is depends on the luminescence properties of the carried out by erasing the latent luminescence sample, especially luminescence intensity. Re- and then measuring the apparent palaeodose ported values range between relative standard Fig.
Where the apparent palaeodose is deviations of a few percent, e. However, it is possible that the phenomenon of thermal transfer is also present and in this case a compromise between a preheat procedure suitable to remove all un- stable charge but without causing significant thermal transfer is necessary.
For feldspar samples, storage tests are carried out to monitor the short-term stability of the artificially-induced luminescence signal. This is carried out because feldspars can sometimes be affected by a phenomenon referred to as anomalous fading that describes a loss of signal with time WINTLE see section 6.
The increase of apparent palaeodose results from an OSL signal that is induced by ther- After obtaining the palaeodose, the next step mal transfer of electrons from light-insensitive to in age determination for a sample requires as- light-sensitive traps. Similar to Abb.
In most tiert aus einem OSL Signal, welches durch thermi- cases, the accumulated dose per unit time, the schen Transfer von Elektronen aus lichtinsensitiven dose rate, is constant and the age t of a sample in lichtsensitive Fallen hervorgerufen wird.
A minor com- charge from hard-to-bleach to easy-to-bleach ponent of the dose rate is produced by ionising traps. Most studies that have reported signifi- cosmic radiation and can be estimated from cant thermal transfer are related to quartz with geographic position and burial depth of the a young sedimentary history, i.
The test described above rate a directly in the sediment using dosim- is a quick and effective way to exclude the eters, b by measuring alpha, beta and gamma presence of thermal transfer. For this, tablished conversion factors. In practice, most the palaeodose is determined for a series of laboratories use the last approach. Within the different preheat temperatures Fig. Furthermore, the panded.
Calculated in time. Moisture for radionuclide analysis in this context cf. Most commonly necessary to consider the radiation attenuation used are inductively-coupled-plasma mass- by pore water. Inhomogeneity due to grain size, spectrometry ICP-MShigh-resolution gamma pore volume and moisture distributions, as well spectrometry, neutron activation analysis NAA as of the mineral composition are removed in and flame photometry for K only.
To check the multi-grain samples by averaging over a large performance of the procedures certified refer- number of grains. An inhomogeneity remains ence materials are available for all methods. The disadvantages the grain the external dose. This effect is dealt of ICP-MS are: a small sample size can be a problem if the sediment exposure is inhomo- geneous, b total dissolution of the sample, especially if zircon is present, is not straight- forward, c measuring K by ICP-MS is rather problematic cf.
High-resolution gamma spectrometry is rather time-intensive each measurement takes at least a day and requires usually at least g of sample material. Larger sample sizes do, however, reduce uncertainty due to inhomoge- neity.
The most important advantage of gamma spectrometry is related to the assessment of pos- Fig. In this The internal dose rate contribution is usually example, palaeodose remains constant for preheat considered to be negligible for quartz grains. In K-feldspars it is often estimated from the stoichiometry of the mineral. In single aliquot dating, the technique now used by the majority of luminescence dating laboratories, the palaeodose is assessed from many replicated single aliquots. Sev- eral statistical methods have been developed to analyse luminescence data and determine the palaeodose.
For those samples shown to be completely bleached prior to deposition, some form of central tendency approach is used such as weighted arithmetic mean, median or a central age model cf.
For the palaeodose val- ues determined using any of these approaches standard deviation and standard error are then determined cf. For incompletely bleached samples determination of the pal- aeodose is more complex see sections 6.
For dose rate calculation, the results of Fig. Longitude has a negligible have also to be considered see sections 5. The lower x-axis gives and 6. These quite complex calculations are absolute values while the upper x-axis indicates the usually carried out using special computer pro- relative contribution from cosmic rays for a generic sample reflecting a typical sediment with a mean grams such as AGE by R.
Kuhlig, Freiberg. For all such deposits it is mandatory to investigate if the sample has been completely Once both the palaeodose and all dose-rate bleached prior to deposition or not and several relevant information are available the lumi- approaches exist for doing so. Luminescence dating: basics, methods and applications The alternative and recently more widely used approach is based on the assumption that sediment grains are not only incompletely, but differentially bleached prior to deposi- tion.
This means that the luminescence signal may be completely bleached in some of the grains while the remaining may carry varying amounts of residual signal.
Luminescence dating: basics, methods and applications. Luminescence dating: basics, methods and applications F RANK P REUSSER, D ETLEV D EGERING, M ARKUS F UCHS, A LEXANDRA H ILGERS, A NNETTE K ADEREIT, N ICOLE K LASEN, M ATTHIAS K RBETSCHEK, D. The application of luminescence methods requires an understanding of the nature of glacial and associated environments to select the most appropriate sediment samples for dating.
When measuring several individual grains from a sample, the lower values in a distribution of doses will most likely represent the grains that were zeroed while the upper values in the distribu- tion will reflect grains that had residual lumi- Fig.
Although many studies from an unstable signal component. Das Vorhandensein eines Aus- for identifying completely bleached samples leuchtplateaus belegt jedoch nicht zweifelsfrei, dass FUCHS et al. To One approach is to plot palaeodose as a func- determine the true burial palaeodose the dose tion of optical stimulation time in the case of distribution must be investigated further, and OSL and IRSL or temperature in the case of for this, it is necessary to measure at least a few TL.
The basic idea behind this approach is dozen individual palaeodose estimates to en- that the signal during initial stimulation and sure a substantial statistical basis. For time temperature for incompletely bleached the time being we have to consider that none samples and a flat shine-plateau-plot for of the approaches has proven to ubiquitously samples that were completely reset at deposi- provide the correct result when compared to tion Fig.
Unfortunately, this approach independent age control. Dating results for has not been proven to ubiquitously identify samples taken from certain environments, in incomplete bleaching e.
Hence, a flat shine-plateau may only be ered carefully until more sophisticated methods interpreted as evidence for, but not proof of are available. As each sample has its own sedi- complete bleaching.
For alluvial sediments, several case studies have shown that the coarser grains appear to be better bleached than finer fractions e. While sample a displays the individual estimates, the causes of which a symmetric distribution with only two aliquots ha- are not all fully understood or quantified at ving significantly higher doses, aliquots of sample present.
One major demand in luminescence b show a large scatter in palaeodose values. One important issue in this context cross-check the results, and will in most cases is that the spread in palaeodose is very much help to prove if the age can be considered reli- dependent on the number of grains on the mea- able or needs to be interpreted with caution. With regard Earlier studies also explored the lower light to aliquot size, it is also important to recognise sensitivity of TL compared to optical signals.
The most common effect of pedotur- hence, the luminescence signal from small bation will be contamination of older sediment aliquots most likely originates from a few or by younger surficial material. This will cause a even single grains only. For large aliquots, negatively skewed dose distribution where the containing several hundred or thousand of lower palaeodose values are not representative grains, the variation of natural palaeodose will of the variation in true burial dose.
In contrast, be relatively small, whereas for small aliquots partial bleaching will cause a positively skewed the variation will increase, and for single grains dose distribution where the true burial dose lies will increase still further. For example, the vari- in the lower dose region, while the upper part ation in palaeodose values observed for some of the distribution represents grains that where fine-grain aliquots, which contain hundreds of incompletely zeroed at deposition.
This occurs due to the fact al. Although the majority of causes of measurement; b partial bleaching; c post- natural variation of palaeodose are difficult to depositional sediment mixing caused by biotur- constrain, it is likely that the effect of microdo- bation or similar phenomena; and d variation simetry may be inversely related to the number in the distribution of radioactivity within the of hotspots within the sediment matrix.
MAYYA sediment microdosimetry.
This is much less than the spread of palaeodose values observed 6. Incomplete bleaching of the luminescence signal, as discussed above, The phenomenon of anomalous fading was first can result in a substantial scatter of palaeodose observed by WINTLE in a study of TL values resulting in overestimation of OSL ages. Pedoturbation by the majority of electrons in the trap. With regard to the latter, two issues are of major relevance.
Firstly, the thermal pre- treatment must be long enough, and the tem- perature high enough to remove thermally un- stable components. This same unstable signal is not allow transmission of emissions in a very nar- present in the natural sample and, as a consequence, row band. While studies implementing these the absorbed palaeodose and hence the age of the recommendations often produce ages consis- sample will be underestimated. Daraus ages e.
The measurement of feldspars of volcanic origin, same artificial radiation dose will produce a which have been shown to be predominantly much higher signal than that resulting from affected by fading, and may be due to the natural irradiation and, as a consequence, the disordered crystal lattice in volcanic minerals palaeodose will be underestimated as will the resulting from rapid cooling and crystallisation age of the sample Fig. This may also explain the fad- Preheating the samples prior to measurement ing observed in volcanic quartz.
Where electrons e. More research in this that is often found in the feldspar fraction, but area is necessary to fully utilise the potential of is not relevant for palaeodose determination. An feldspars in dating; in particular the higher satu- extended chemical analysis e. K, Na, Ca, Al, ration dose and hence increased dating range. Si concentrationthe use of micro-probe equip- ment and the calculation of a theoretical feldspar 6.
Besides the problems associated with the de- termination of the dose absorbed during burial 6. Water in the sediment pores absorbs much more radiation than air and so the effective 6. For sand-size minerals, for which most re- The present moisture content of the sample search has concentrated during the last decade, is often used as a guideline for age calcula- a-values are of minor importance as alpha tion but it is crucial that potential changes particles penetrate only the outer ca.
It is often also usually removed by HF etching during sample preparation. When measuring fine-silt grains, for example when dating loess, lacustrine sedi- ments or fine silicate inclusions from ceramics, the the a-value is of major importance. For such materials it is recommended that the a-value is determined for each individual sample, which involves comparison of laboratory-induced luminescence due to both alpha and beta radia- tion e.
K-concentration where chemical analyses e. AAS or beta counting are used, and is is due Abb. Special attention must be directed to sediments In such cases the sediment may be above the exhibiting radioactive disequilibria since the water table for a significant part of the burial prerequisite of constant radionuclide concen- period and pores may be only partially filled trations does not hold cf.
In lacustrine settings, pore space Their half-lives Uncertainties related to sediment moisture are are of the order of to years and thus most important for water-laingives sediments but they the physical andare still present chemical in nature. In an undisturbedseveral daughter isotopes of various elements geological situation the activities within each deca but with half-life times much shorter than 6. Physical and Open syst erosion and accumulation results in variation chemical differentiation processes lead to a loss stationary of the thickness of the overburden states above a ifofgeochemical this balance and properties do notdisequilibria.
As a buried sediment sample. Therefore, the contri- In closed systems the balance is restored on a the dose bution of cosmic rays to the total timerate dependent of timechange scale ofin theactivities in five order of ca. Open systems can external dose of burial time, but may vary significantly. Suchratereach also becomes stationary astatesfunction that variesproper- if geochemical with time. Equatio fluctuation in the overburden thickness is less ties do not change with time.
As a consequence be replaced significant in sedimentary environments by anofiteration where techniquechange the time dependent whichinsearches forthethe point in t activities in the contribution of cosmic rays to the total dose case of radioactive disequilibria, the external is generally low.
However in quartz- with time. In cosmic dose contribution is calculated using the case of radioactive disequilibria one needs: present sampling depth. To provide a more ac- a preferably an analysis of all long-lived ra- where t0 is the moment of sample bleaching. From these mostly fulfilling criterium a. Modelling the disequilibrium in the past is Especially for fine grain dating, the dosi- based upon assumptions concerning the value metric consequence of variable moisture of the prevailing parameters and their vari- is a variable attenuation of the external ir- ability with time.
In most cases this results in radiation with time.
Luminescence dating basics methods and applications
The resulting enhanced a more or less broad range of possible time uncertainty in the dating result can only be evolutions, leading to the current radionuclide reduced by applying a model considering concentrations. Reasonable explanations of the mod- shown.
However, it is often only through lumi- ern radionuclide contents partly require the nescence on heated materials that an age of an assumption of an open system, mainly con- archaeological event can directly be provided nected with uranium uptake after deposition.
A careful investigation should include samples in luminescence dating, together with the calculation of borderline cases to give an the appropriate method and the event dated, impression of the likely span of reliable ages which is sometimes not evident at first sight. Or in nescence dating had focused on fundamental the case of dating rock surfaces, the time since problems and the application of TL for dating the last exposure to light is dated, which can heated objects and volcanic deposits as well as be the time of construction or destruction of a some initial work on TL dating of sediments monument.
Ceramics could be much younger cf. Since the introduction of than an associated construction or much older, optical dating using IR and visible light most e. The depositional age of sediment mate change as well as archaeology Table 3, infill provides age information concerning 4. General overviews on early work are pro- abandonment rather than construction, e. Anthropogenic sediments or KEN or STOKES and the following sediments altered by human occupation are sections will concentrate on benchmark publi- difficult to date with luminescence methods.
It is therefore often advisable to select more suitable sedimentological units bracketing the 7. Apart from Heated rocks are usually dated by TL but if the unheated sediments see section 7. In such cases, bleaching can be distinguished: 1 heated sediment e. Conversely, other rock materials. An additional category TL of flint is very hard to bleach by light for includes man made materials such as slag and most samples from a highly diverse material walls constructed from rock materials.
It is ages by calibrating radiocarbon data, the ap- possible to establish the authenticity of figu- plication of TL dating of ceramics and pottery rines and ceramics using TL and OSL, although became less important from the s onward.
The site of Pedra Furada is the other hand that the accuracy of chronolo- controversial because of the claim that it has gies based on fabric only required refinement a much greater antiquity than the time gener- BARNETT The feasibility of using TL for fire places, hearths or fire pits, which lie close dating heated limestone is reported by ROQUE to an archaeological settlement site but lack et al.
While the TL age for the heated difference between archaeological material sediment agrees well with radiocarbon data, surrounding the intrusive burial and skeletal the TL result for the pit infill is greatly over- material is negligible. Heated flints from layers estimated and clearly shows that this method containing Middle Palaeolithic artefacts in sev- is inappropriate for unheated sediment. These and confirming the likely function of the fire dates provide evidence for an extended overlap pits for early copper smelting technology.
Recently, a SAR is often questioned. Mastering fire is regarded Determining the age when a wall was built, a as one of the hallmarks in human evolution and megalith was erected, repair work or destruc- certainly played an important role in dramatic tion took place, or even when rocks were changes in human behaviour connected with moved and discarded or reused is of great diet, defence and social interaction.
Analysis of importance in archaeology. These results were contrasted by the al. TL dating of heated flint can also be surface exposure age of rocks which were un- used to verify the integrity of an archaeological moved for several years. But even standard site or layer. It has been 7. Despite the fact that anomalous fad- derestimation of TL e. A comprehensive review on minerals to be transmitted. TL dates have with independent age control and geological been used to establish chronological frame- time models it also became evident that the ap- works for volcanic activity in areas such as plication of luminescence both TL and optical the Massif Central, France VERNET et al.
An particular for quartz, has been applied to loess important ct is the use of the red emission to improve both the precision and reliability of from feldspar, which has proven to be more the chronology as well as to extend the dat- stable than other TL emissions e. However, rela- tiple-aliquot silt-size polymineral IRSL and tively little research has been carried out and to TL on samples from a site in Czech Republic.
They produced reliabile quartz ages as old as ka with independent age control Loess was among the first sediments that were from tephra chronology. Polymineral fine-grain systematically dated by luminescence methods, ages, which have been measured using the UV in particular by TL e.
This total bleach approach comprehensive summary of previous work on assumes that all light-sensitive TL is removed luminescence dating of Chinese loess is pro- from the grains during transportation and this vided by STEVENS et al. The latter in particular looks rather dose distributions and hence in improving the promising, with WANG et al.
Aeolian deposits are also important 7. Some of the oldest to sufficient light for optical re-setting of the luminescence ages in this case TL ever pub- luminescence signal prior to burial, and so lished have been determined for stranded beach poor bleaching is rarely a problem in aeolian dunes from SE Australia that yielded ages as materials DULLER Since then, tuyama chron.
TOW et al. As already indicated dating results. The necessity of an increase of by DULLERit was demonstrated that samples analysed per dune as well as the inves- samples not fully zeroed consist of a mixture tigation of several dunes within a dune field to of grains having a different degree of bleach- obtain not only detailed but informative records ing, including grains that have been completely of aeolian processes in a certain area have been bleached at deposition.
The combination broad and positively skewed for incompletely of ground-penetrating radar GPR and OSL bleached samples, and tight and normally dis- dating provides a powerful tool to reveal the tributed for well-bleached samples cf. Based on the GPR et al. A comprehensive review on profiles of the internal structure of the dunes the problems and potential of optical dating of sampling locations for OSL dating can be de- fluvial deposits has been provided by WALLINGA termined e.
With the advent of OSL methodology the River Loire downstream from the source, with dating of waterlain sediments was reconsidered, values close to zero for transport distances of but took nearly a decade from the breakthrough more than km.
Nev- ent resetting for individual components of the ertheless, up to the late s fluvial and in par- OSL signal. FUCHS et al. These authors been considered questionable at least. One of the pioneering studies was that 0. Many of these Danube, parts of which were deposited by the processes cause downslope movement of sedi- floods in For some of these samples re- ment as a rather compact block such as in the sidual ages are as high as several 10 ka.
How- case of sliding. Hence, with respect to daylight ever, these exceptional values are probably bleaching, only a small fraction of the sediment the result of an artificial input of sediment to in the colluviation process i.
Luminescence dating: basics, methods and applications It was demonstrated that the underestimation of IRSL ages was due to anomalous fading that was observed in storage tests. Abstract: Luminescence dating is a tool frequently used for age determination of Quaternary materials such as archaeological artefacts, volcanic deposits and a variety of sediments from different environmental settings. The present paper gives an overview of the physical basics of luminescence dating, the necessaryCited by: Luminescence dating: basics, methods and applications 99 nal dose rate to the total dose rate is usually considered to be negligible. External dose rate comprises all radiation acting on the luminescent grain from the surrounding sediment, and is derived from 40 K, abundant in some feldspars, micas and clay minerals, and the isotopes of the U/ U and Th decay chains.
If material is transported applied to the reconstruction of the fluvial his- by water e. Another problem is related to coagula- et al. Firstly, hillslope de- posits are usually repeatedly reworked, which The term hillslope deposits describes sedi- increases the probability of daylight exposure. Such deposits are often re- daylight before the sediment grains are eroded ferred to as colluvium although the term is in- and transported. Nevertheless, investigating consistently used by different researchers.
First the degree of bleaching prior to deposition, successful studies on dating colluvial samples as described in section 6. Similar studies have as vertical displacement along faults scarp been carried out, for example, in Romania KA- leads to its erosional degradation. These 7. PORAT et al. Both studies have highlighted scarps. Studies in a similar context have been the potential as well as the limitations of TL. Widespread clearance experimentally investigated the bleaching of of woodlands and associated soil erosion sediment in suspension demonstrating that the typically causes increased erosion along hill- optical signal is almost completely bleached slopes, for example, when humans established in dilute suspensions within a few hours, little permanent settlements and agriculture.
Among bleaching has been observed in dense suspen- the first studies was that by LANG who sions. A frequency dis- aeodose De measurements being attributed to tribution of IRSL ages from the area revealed different bleaching characteristics of the differ- that increased colluviation coincides with ent emission bands.
Colluviation strongly fluctu- lacustrine deposits from Greece revealing an ated in the course of the Holocene, with a sharp underestimation of polymineral fine grain IRSL increase during the Early Neolithic and the and post-IR OSL UV emissions compared to onset of agricultural activities. Further periods quartz OSL ages and radiocarbon chronology. However, from the Western Washington, British Colum- the presence of fading is probably explained bia and Toronto area.
Further inves- tuned to regional insolation. The particular advantages of lumines- Switzerland were completely bleached while cence are that it circumvents contamination those from Northern Germany were not, for problems that often affect radiocarbon in arid most samples investigated. These results were environments and extends the dating range be- additionally supported by further investigations yond the few 10 ka possible with radiocarbon. Beside the problem of AGE et al.
OSL dating of glaciogenic deposits from 7. Optical dating of proglacial ages of Late Glacial sediments applying dif- and glaciofluvial sediments from inneralpine ferent bleaching techniques. While samples from the in- that ages consistent with stratigraphy are ob- neralpine valleys can be assigned to bleaching tained when blue TL emissions are used for type B DULLERincompletely bleached dating.
In another positively skewed distribution, failed due to the early study, MAUZ et al. This is sup- quartz separates to date littoral deposits from ported by investigations of FUCHS et al. Therefore, frequency distributions should inner shelf deposits.
Ad- quartz TL dating for relatively high sea-level ditionally, quartz samples from the northern m during early MIS 3 ca. Applying SAR- methodology to Guinea. Nevertheless, for those deposited by turbid water suspension. DULLER concluded that the single grain The author also highlights the potential prob- methodology is the method of choice to detect lem associated with estimating the correct av- partial bleaching.
HONG et al. The Region France, Belgium. However, TL ages of older affect in such environments. OLLEY et al. This question els of signal resetting in different regions. These authors observed a sensitivity of the natural signal at the beginning good agreement between OSL and radiocarbon of the SAR procedure, which is not corrected age from bivalve mollusc shells, although ra- for, contamination of the stable fast component diocarbon ages on bulk sediment samples were of the OSL signal by less-stable components between and a higher than OSL and as well as open system radionuclide behaviour bivalve ages.
The incorporation of reworked and inaccurate estimates of long-term water material in the bulk samples is suggested as the content. Lu- two cores from the Arabian Sea where age con- minescence dating represents a suite of related trol is provided by radiocarbon, tephrachronol- techniques, all of which provide an estimate of ogy and a correlative marine-proxy age model.
EN, S. For palaeodose deter- Geochronology, 2: Furthermore, it is expected that ment-time dependent single-aliquot equivalent- it may be possible to extend the upper dating dose estimates from quartz in the identification limit using approaches such as thermally-trans- of incomplete signal resetting.
With regard to dose rate of measurement-time-dependent single-aliquot determination, improvements in the handling of equivalent-dose estimates using predictions radioactive disequilibria and variation in sedi- from a simple empirical model.
Reviews, BELL, W.
Luminescence Dating Basics Methods And Applications, ausbildungs speed dating aachen, boys looking for men on a dating, singleborse hildesheim. Date d'inscription Taille. Entre / Aug 24, Luminescence dating (including thermoluminescence and optically stimulated luminescence) is a type of dating methodology that measures the amount of light emitted from energy stored in certain rock types and derived soils to obtain an absolute date . Principles of luminescence dating Luminescence behavior of dielectric materials used in dating. Luminescence dating equation. Electron trapping mechanisms. Natural sources of ionizing simplybeyondexpectations.com: Ken Munyikwa.
Thermoluminescence and related phenomena. When optical excitation begins the latent luminescence in the mineral will start to decay, resulting in a so-called decay curve recorded by the photomultiplier Fig. Stimulation by visible light is conducted by exposing the sample to a laser beam, the light of a filtered halogen lamp or to high-power light emitting diodes LEDsthe latter being the latest and most versatile development, and hence used in the majority of currently manufactured luminescence readers Fig.
The width of the excitation waveband differs for different stimulation sources but all lie in the green to blue part of the spectrum, i. Both quartz and feldspar respond to stimulation within this waveband although for dating applications it is principally used for OSL measurements of quartz.
Light of longer wavelengths becomes increasingly inefficient at stimulating OSL in quartz, whereas wavelengths in the near infrared excite luminescence in feldspars due to one or more excitation resonances.
Light emissions for OSL from quartz are detected in the ultraviolet range. Stimulation uses either an IR laser or IR diodes, the latter now being the most commonly used. The fact that quartz does not respond to IR stimulation is regularly used to check quartz-separates for feldspar contamination. Recent research has focused on IRSL red emissions and it is expected that the apparent stability of the IRSL signal in this part of the spectrum may overcome problems related to signal stability, i.
Spectral measurements in this study identified a very low stability of the red about nm IRSL emission of feldspars. An emission at nm during excitation by ionising radiation is typical for potassium feldspars orthoclase, microcline only.
The physical basis of this phenomenon and methodological cts of its application in dating were investigated to develop a reliable new technique for age determination of sediments SCHILLES et al. The IR emission can be interpreted as the transition of electrons from the conduction band into a particular kind of electron trap.
During ionising irradiation a number of electrons reach the conduction band from which they promptly recombine with luminescence centres and emit visible VIS fluorescence or transfer to that electron trap by emission of near-IR fluorescence cf. Firstly it is a direct measure of the electron density of a well defined trap, which does not rely on the conventional luminescence centres which, as shown, can fade.
Another advantage of this method is that luminescence stimulation and dose accumulation are applied at the same time. This allows continuous measurement and the recording of a very high number of dose points Fig. Furthermore, single aliquot regeneration procedures see Section 5.
The measurement of an IR luminescence emission itself however, together with its low dynamic range and the special procedure of dose application and measurement is not a simple task and requires special instrumentation ERFURT et al.
Its dating-range spans 20 ka to about ka in most cases and as far back as ka with low dose rates. It has so far been applied to sediment dating where the signal is optically reset but can also be used to date thermally reset events. Developments in instrumentation including the application of single grain dating, for which the first successful experiments have been made, will improve this method with regard to its precision and the potential to extend the age range.
The result of this slow increase of stimulation intensity is that in quartz the trapped charge is released first from shallow, and subsequently to deeper traps. This procedure results in overlapping peaks of luminescence emission related to different traps in some sense similar to TL peaks. Due to the overlap of different components it is necessary to apply mathematical deconvolution to the LM-OSL data to discriminate between different components cf.
The result of this fitting gives information on the presence of different OSL components in a particular sample Fig. Fast, medium and slow components have been identified, with the latter consisting of up to five individual subcomponents JAIN et al. The first of these is the fastest emission and it follows that this is the easiest to optically bleach in the natural sedimentary environment. Whether or not these different components originate from the same or different optical charge traps is still not fully understood.
It is important to note that not all components are present in quartz of different geological origin Fig. Furthermore, due to uncertainties related to mathematical deconvolution, LM-OSL has rarely been used for direct dating purposes. Note the high number of dose points and how the bottom curve residual: deviations from the fitted line shows good agreement to the fitted stretched-single -exponential decay curve.
Similar to sediment dating, the aim is to determine the time when a stone surface was last exposed to daylight.
Aspects of Archaeology: Thermoluminescence Dating
The upper and lower surface of a granitic block, for example, will be shielded from daylight after erecting the wall of a historic monument. Dating the last daylight exposure of mineral grains within construction material hence reflects the age of a building.
Besides archaeology, the approach also has great potential for geological applications, as sediments often contain pebbles and boulders. Optical dating of stone surfaces requires new approaches to sample preparation, palaeodose measurement and dose rate determination. In contrast to conventional luminescence dating, stone surfaces are kept intact to ensure only the grains exposed to light during the construction process are analysed.
Because samples remain intact, this method has the great advantage that all information on the micro-dosimetric field is preserved; a detail which is destroyed during the traditional sample preparation.
However, the conventional way of measuring bulk luminescence signals using a photomultiplier tube is not appropriate for a stone surface with varying minerals and grain-size. This produces a large amount of data several thousand data points per individual measurement and data management and analysis require a special software program GREILICH et al.
This software allows production of palaeodose values for each of the many picture elements, filtering of data and statistical analyses that can be spatially resolved for each pixel and then displayed in histograms. Luminescence dating: basics, methods and applications Fig. The fast component that dominates the signal in sample a is not present in sample bwhich is dominated by an unstable medium component.
Die schnelle Komponente die das Signal in Probe a dominiert ist in Probe b nicht vorhanden; diese wird durch eine instabile mittlere Komponente dominiert. This is achieved by using an energy dispersive X-ray analysis detector mounted on a scanning electron microscope SEM-EDX for the determination of the potassium content of feldspar grains.
A special variant of fission-track analysis using tracks induced by fast neutrons is used to determine dose rates from uranium and thorium WAGNER et al. From the spatially-resolved palaeodose and dose-rate data, luminescence ages are calculated for each of the analysed grains from a drill-core surfaceslice. The last daylight exposure of a stone surface is calculated by combining data of several individually drilled samples.
After the OSL traps are emptied through light exposurethe transfer from the refuge traps into the OSL traps is generated by thermal treatment. In contrast, the basic transfer signal derives from electrons trapped in light-insensitive traps and is released into light-sensitive traps by preheating and therefore inapplicable for dating. WANG et al. These values are either associated with the determination of palaeodose and the reliability of this measurement or are used for the calculation of a dose rate.
The following section gives a brief overview of how these values are determined, how they are taken into account in the age model and which values give information on the reliability of the applied dating procedures.
It is mandatory to collect detailed information on the geological context including photographs, detailed field notes and so forthparticularly concerning the environment of sedimentary deposition and sediment overburden sample depth below surface, indication for post-sedimentary disturbance, hiatuses, sedimentation cycles. Present and past hydrological conditions sediment moisture of the sample need to be assessed as far as possible. To ensure a uniform radiation field, the sample should be taken from a homogenous layer with a thickness of at least 50 cm.
If no such layer is available, on-site measurement of gamma radiation using a portable gamma spectrometer or a gamma counter should be utilised to minimise the impact of inhomogeneity on dose rate calculation. Samples used for the determination of palaeodose have to be taken without exposing the material to daylight, and is usually achieved by forcing opaque metal or plastic tubes into a freshly cleaned exposure.
Material from both ends of the tubes, which is likely to have had some daylight exposure, is discarded for palaeodose measurements but can be used for dose rate determination. Some laboratories require additional material for dose rate determination, particularly when high-resolution gamma spectrometry measurements are performed, but this. For sand sized grains, quartz and K-feldspar separates are isolated using heavy liquids with densities of 2. Alternatively, one can also use polymineral fine-grain samples for palaeodose determination.
In such samples the IRSL signal will usually be dominated by feldspar emissions as quartz is not sensitive to Luminescence dating: basics, methods and applications material need not be protected from daylight exposure.
It is strongly recommended that researchers having little experience in sampling for luminescence dating should contact an expert prior to sample collection to get information on specific requirements. All preparation work for the determination of the palaeodose is carried out under subdued laboratory illumination to avoid any loss of luminescence.
Most luminescence facilities have either red or orange low intensity lights installed. The first steps include treatment by HCl and H2 O2 to remove carbonates and organic material, respectively, always followed by washing with deionised water. A particular grain size is then isolated by Fig. Different laboratory doses are added to the natural signal NL to characterise the increase of luminescence intensity with dose.
The low dynamic range of the IR-RF signal can also be seen. Pages you may also like. You can also read. Operating Guide. Select All. Next part