Parameters to check the accuracy of mostly regenerative measurement protocols (like the SAR protocol). Only if the data acquired for a sample or an aliquot passes these criteria, it is considered for further evaluation, otherwise it is discarded. Acceptance criteria are e.g. the dose recovery test, the recycling ratio, the recuperation ratio or the IR depletion ratio. The acceptable limits set for certain criteria are arbitrary (e.g. recycling ratio 0.9 and < 1.1; Murray & Wintle 2000), but should be identical between laboratories to ensure comparability of data.
With regard to electrons as charge carriers, acceptors are defects in the crystal lattice that have too much negative charge and can thus more easily release an electron than regular atoms in the structure. In the energy band model, they act as hole traps and are responsible for the emitted luminescence (‘recombination center’).
It describes the “truthfulness” of a measurement, i.e. the degree to which the measured value coincides with the (unknown) true value. Low accuracy in measurements is related to systematic, directed errors, i.e. the accuracy of a measurement cannot be increased by enlarging the database. A measurement can result in an accurate value with low precision (high scatter) and vice versa (Wagner 1998; Geyh 2005).
Phosphorescence emitted by a sample after irradiation; it persists 10-6 s (up to several hours) after end of irradiation (Chen & KcKeever 1997).
Equation for calculating a final luminesce age, consisting of the equivalent dose De in the numerator and the dose rate D ? (which should be representative for the dated period) in the denominator. The De to insert may be derived from statistical modeling (see Age models) of multiple individual De’s from one sample. The dose rate includes the moisture-corrected alpha-, beta-, gamma and cosmic contribution, while some of them may be negligible, depending of the sample’s context and environment (e.g. the alpha-contribution using the quartz inclusion technique).
Statistical models aimed at extracting the ‘true’ age (or burial dose) out of a distribution of ages/doses of individual aliquots. Especially for overdispersed or multimodal age/dose distributions, these models may help to separate distinct age/dose populations. The procedure to decide which one of the plenty age models to use can be based either on sole statistical numbers (such as skewness and kurtosis of the distribution; Bailey & Arnold 2006; Arnold et al. 2007) or on consideration of the sample’s environment (transport mode, section characteristics etc.; Galbraith & Roberts 2012).
A subsample of the material to be measured. Aliquots can be of different size (different number of coarse grains): Decisive factors are the brightness of the sample and the bleaching history. Especially for poorly bleached samples or those with several dose populations, the use of small aliquots delivers more detailed and accurate information on the last resetting event
Method to determine the dose rate from U and Th by measuring the alpha activity of a sample. A layer ( 50 Mm) of finely ground sediment (Zöller & Pernicka 1989) is brought in direct contact to a scintillation screen (e.g. ZnS) that emits a small light flash (scintillation) when hit by an alpha particle. The scintillation events are counted by a photomultiplier, and the dose rate derived from U and Th can be calculated from the measured alpha activity. The relation between U and Th concentrations in sample may be deduced from the number of counted ‘pairs’, i.e. alpha decays that occur within 0.2 s. These pairs are generated when Po-216 disintegrates into Pb-212 (half-life of 0.145 s) in the Th decay chain. The major advantage of alpha counting is its simplicity and reliability. However, the dose rate due to K must be determined using another analytical technique (e.g. gamma-spectrometry, ICP-MS).
Corpuscular radiation emitted from atoms when undergoing radioactive decay. Alpha particles are helium nuclei (two protons and two neutrons) having a discrete energy spectrum. Due to their high mass, alpha particles have a high ionization density, but are stopped in matter (2.6 g/ccm) within about 20 µm, depending on energy. The energy spectrum of alpha particles present in natural environments ranges from 0 to 8.8 MeV, while for laboratory irradiation, mono-energetic radiation is used (e.g. 3.7 MeV particles from 241Am). Since alpha radiation produces less luminescence per Gy than does beta or gamma radiation, the alpha effectiveness (see k-value, a-value, b-value) has to be determined whenever alpha radiation contributes to the dose rate.
Oxide of the element aluminium (Al2O3) with strong luminescence. This material is routinely used in environmental or medical dosimetry in a doped form (Al2O3:C) due to its high luminescence sensitivity (Kalchgruber 2002; Richter et al. 2010).
Heating the sample to high temperatures (usually 400-900 °C) in order to release any previously accumulated charge from the traps.
Room-temperature signal loss of IR-stimulated luminescence of K-feldspars over time which cannot be explained by the physical parameters (trap depth, frequency factor) of associated electron traps (Wintle 1973). Over the last decades several concepts have evolved for the explanation of both athermal and thermally assisted fading (e.g. Visocekas 1985; XXXX ….); the most prominent being quantum-mechanical electron tunneling. With certain limits, fading follows logarithmic decay (i.e. constant percentage of signal loss per decade). To avoid age underestimation, fading needs to be determined and corrected for each sample using e.g. the g-value concept (Huntley & Lamothe 2001). There are, however, alternative approaches of K-feldspar dating without the need for fading correction (Molodkov et al. 2007).
Luminescence of shorter wavelength than the stimulation wavelength (usually measured in the course of OSL and IRSL dating, e.g. blue or green stimulating light and detection in the UV) (Aitken 1998).
Attenuation of radiation
While traversing matter, radiation (both corpuscular and electromagnetic radiation) is attenuated through interaction with the crossed material. The absorption of radiation can be described by particles (e.g. alpha particles) slowing down through collisions with atoms or reduction of the field energy of electromagnetic radiation. According to Lambert’s law, the intensity of incident radiation reduces exponentially with thickness of traversed matter.
Build-up of dose by radiation coming from the sample itself (i.e. internal dose rate only). This is the case for minerals containing high amounts of radionuclides; for instance, zircon (U concentration of 10-1000 ppm) builds up a measurable auto-regenerated signal within a few weeks (Templer 1985). Here, the external dose rate is negligible and an age can be determined without the need for artificial irradiation (which would be inaccurate, anyway, due to zoning of zircons).
Value expressing the efficiency of luminescence production of alpha radiation in comparison to beta- or gamma-radiation. In contrast to the k-value system (comparing luminescence resulting from alpha- and beta-doses), the a-value is based on the fact that the luminescence production is approximately proportional to the generated alpha track length. The difficulties related to the energy dependence of the k-value are thus circumvented (Aitken 1985). The original definition of the a-value is a = x/(13S), where x is the dose in Gy required to produce the same amount of luminescence as 1 minute of irradiation with a source of strength S (Aitken 1985). The source strength is given in units µm µm-3 min-1 = µm-2 min-1 (generated track length per volume and time). For quartz, the a-value is identical to the k-value using 3.7 MeV alpha-particles for irradiation.
The part of the recorded signal that does not originate from the luminescence sample. To obtain the net signal of the sample, the background has to be subtracted from the bulk signal. The background is usually measured on annealed aliquots (TL, repeating the measurement) or bleached aliquots (OSL, using the later part of the measurement curve which is assumed to contain background signal only).
In the energy band model, the band gap describes the energetic distance between the upper boundary of the valence band and the lower boundary of the conduction band. In ideal crystals, electrons are not allowed to stay there. Lattice imperfections, however, create electronic states in the band gap that form the basis of the luminescence phenomenon.
Beta radiation consists of electrons and is the result of atoms undergoing radioactive decay (beta-minus decay). This type of radiation belongs to the group of slightly ionizing radiation (in contrast to alpha radiation) and travels up to 2 mm in matter of density 2.5 g/ccm. The energy spectrum is continuous with a specific maximum energy for each decaying nucleus (in the order of 1 MeV).
Exposition of the sample to natural sunlight or artificial light sources in order to remove charge from optically sensitive traps.
If a charge carrier is decelerated, electromagnetic radiation (the so-called bremsstrahlung) is emitted due to energy conservation. This is e.g. the case when beta radiation is attenuated in matter.
Value expressing the efficiency of luminescence production of alpha radiation in comparison to beta- or gamma-radiation. As the a-value, the b-value system operates with generated alpha track length instead of deposited dose. The basic principles of both systems are thus the same, while the b-value is expressed in units Gy m2. Numerically, a-value and b-value are related by b = 13a (Bowman & Huntley 1984).
Center (see Luminescence center)
Grains in the size range of approximately 90-200 µm, usually used in the course of the quartz inclusion technique.
The term component in luminescence dating usually refers to the different constituents of the quartz OSL signal (although two different components are also attributed to the feldspar IRSL signal; Auclair et al. 2003). It has been shown that quartz CW-OSL curves can be best fitted to the sum of several first-order exponentially decaying functions representing different optical depletion rates (Smith & Rhodes 1994; Bailey et al. 1997). These components are most likely related to different electron trap types in quartz which are characterized by varying thermal stability and saturation doses. The best suited component for optical dating is the so-called fast-component due to its rapid optical resetting, low recuperation rates and thermal long-term stability (Singarayer & Bailey 2003; Jain et al. 2003). For reliable dose estimates, it is thus crucial to make sure that the luminescence signal is strongly dominated by the fast-component. Visual assessment of the components’ contribution to the sum signal is provided by LM-OSL measurements or transformation of CW-OSL curves into pseudo-OSL curves (linearly, modulated, hyperbolically modulated, … ; Bos & Wallinga 2012), but component separation (deconvolution) is principally possible with any kind of curve fitting.
Energetic level in the energy band model in which charge carriers (electrons) are able to move freely through the crystal lattice (i.e. they are detached from their host atoms). From here, electrons may be trapped at defects, recombine with luminescence centers or fall back into the valence band.
Cosmic dose rate
Contribution to the total dose rate received by the sample due to cosmic radiation. Through interaction of primary, galactic radiation (e.g. protons, alpha-particles, electrons) with the earth's atmosphere, secondary radiation (e.g. pions, neutrons, protons, myons, electrons) is generated in form of cascades. The composition of the secondary radiation changes with altitude, with mainly myons remaining at sea level due to absorption and interaction of most particles in higher parts of the atmosphere (Krieger 2007). Considering further the influence of the earth's magnetic field, the cosmic contribution to the dose rate is consequently a function of altitude above sea level and geographic coordinates. Long-term variations of cosmic dose rate over the last several hundred ka are unlikely to exceed ~3% und can thus be neglected in most circumstances. With increasing depth below surface, the cosmic radiation rapidly falls off (Prescott & Hutton 1988, 1994). The ‘weak’ component of cosmic radiation (electrons, photons) is absorbed in the first tens of cm of the substrate, so that for deeper buried samples only the hard component (mainly myons) contributes to the dose rate (Aitken 1985).
Cosmic radiation (see cosmic dose rate)
A procedure to numerically/iteratively find parameters of a given function so that this function best fits to the given data (e.g. measurement data).
Cutheat ( see preheat)
OSL/IRSL stimulation mode in which the intensity of illumination is constant throughout measurement time. The resulting OSL/IRSL curve is monotonically decaying.
Sequence of unstable (i.e. radioactive) isotopes in which a daughter isotope emerges from the decay of a mother isotope that in turn disintegrates, and so on. In terms of luminescence dating, there are three relevant decay chains starting with the isotopes U-238, U-235 and Th-232 and ending up in stable lead isotopes (Pb-206, Pb-207, Pb-208). The transition from one element to another occurs while emitting alpha- or beta-radiation.
Separation of individual components from the bulk signal. A means for deconvolution is thought to be curve fitting. For instance, TL and (LM-)OSL curves can be fitted to several individual components which in sum best reproduce the measured data. However, the fitting function is always based on certain kinetic assumptions (e.g. first-order kinetics for the components of an OSL curve).
Defects (in the crystal structure)
Any kind of deviation from the perfect crystal structure. Defects can be divided into intrinsic defects (missing or redundant atoms of the same kind as the regular constituents = vacancies and interstitials, respectively) and impurity-related defects (incorporation of foreign atoms). Defects occur at concentrations of 10E-8 – 10E-7 in common crystals. As charge traps and origin of photon emission, defects play a major role in understanding luminescence of minerals (Wagner 1995; Preusser et al. 2009).
Range of wavelengths (frequencies/energies) in which the luminescence signal is recorded during measurement and used for dose evaluation. Usually, glass or interference filters (or certain combinations thereof) are used to restrict the detected light to the desired spectrum and to block the stimulation light of longer wavelength (in case of OSL).
State in which activities of the decay chain members are not the same, caused e.g. by radon emanation or leaching/enrichment of uranium. In case, input or discharge has ceased, the initial state (equilibrium of activities) is reached after about five half-lives of the respective isotope. Undetected disequilibria (having occurred in the past, mostly in the U-238 decay chain) may lead to erroneous dose rate estimation, and even if disequilibria are registered, dose rate modelling is tedious and based on a bunch of assumptions (Krbetschek et al. 1994; Zander et al. 2007).
Absorbed radiation energy per unit mass [1 Gy = 1 J/kg]
Total radiation dose per unit time to which the sample has been exposed. The unit is usually Gy a-1 or Gy ka-1. Sometimes the term “effective dose rate” is used to express that the quantity has already been corrected for alpha efficiency and/or moisture content.
Dose response curve(see also growth curve)
Amount of luminescence recorded as a function of administered dose, also called <emgrowth curve</em. For equivalent dose determination, the so obtained data points are usually fitted with linear, quadratic or exponentially saturating functions.
DRT (dose recovery test)
Procedure to test the accuracy of a measurement protocol to reliably determine the dose of a specific sample. Here, the natural signal is erased and a known laboratory dose administered which is treated as unknown. Then the De measurement is carried out and the degree of congruence between administered and recovered dose is a measure of the protocol’s accuracy for this sample.
Substance whose properties change in a known way with applied dose. Hence, they can be used to measure or assess the amount of absorbed dose since a defined event of dose resetting. In luminescence dating, mostly natural quartz and feldspar act as dosimeter.
Approach to maximize the contribution of the fast component to the net signal by subtracting a background integral immediately following the initial signal integral. Best results are obtained by choosing the background interval to be 2.5 times the length of the signal integral (Cunningham & Wallinga 2010).
Spectrum of emitted light of a sample during or after stimulation.
Energy band model
Model to visualize the processes of charge transfer in a crystal during irradiation, storage and stimulation. In a crystal structure, electronic states can be depicted as quasi-continuous bands from which only the highest band filled with electrons (valence band) and the lowest empty band (conduction band) are of interest here. Both are separated by a forbidden gap where electrons are not allowed to stay in ideal crystals. The defects of real crystals, however, form discrete energy levels in the forbidden zone, providing meta-stable states for electrons or holes. Irradiation (ionization), charge trapping and eviction as well as recombination can be illustrated by moving charge (electrons, holes) between the bands. For further information on the energy band model, the interested reader is referred to e.g. Aitken 1985 or Bailey 2001.
Environmental dose rate
Dose rate connected to radioactivity outside the mineral (grains) to be dated and to the cosmic dose rate. In contrast to the internal dose rate, the environmental dose rate may undergo temporal changes in its strength.
Equivalent dose (De)
Amount of absorbed dose since the last resetting event
(also called palaeodose)
Signal loss that cannot be explained by thermodynamics (i.e. by the determined kinetic properties of the mineral). The most famous model to explain fading is quantum-mechanical tunneling of charge from the trap to the recombination center (e.g. Visocekas 1985). In feldspar, fading of the IRSL signal is a common observation, while it has not been detected so far for any emission of crystalline quartz. If not accounted for (what is error-prone and disputed), fading leads to age underestimation of luminescence samples.
Loss of signal in percent per decade, also known as g-value. It is used to correct feldspar ages for fading, while the correction should be restricted to the linear part of the dose response curve (Huntley & Lamothe 2001).
Grains in the size range of ca. 4-11 µm, obtained by setting in water or acetone using Stokes’ law. The upper size of fine grains is given by the alpha range in minerals such as quartz, so that grains are fully penetrated by alpha particles. In contrast to the quartz inclusion technique, the external alpha contribution has to be considered in the dose rate calculations.
Mixture of amorphous and micro-/cryptocrystalline silicon dioxide, occurring as nodules in limestone or plates in other sedimentary rocks (there are lots of synonymous words such as chert, hornstone or silex). Due to predictable knapping properties, such material was used for tool production by our ancestors. In case, tools or production waste was heated in antiquity, this event can be dated by luminescence methods (Valladas 1992; Mercier et al. 1995; Richter 2007).
Light emitted from a sample while it is stimulated (e.g. radiofluorescence).
Also called ‚attempt-to-escape‘ frequency and describing the interaction of trapped charge with the host lattice. As a first approximation it can be seen as a constant for each type of trap/center and lies in the range 1E12 – 1E14 1/s. In addition to the trap depth E, it is one of the two fundamental parameters to describe the thermal stability of a trap/center (Furetta 2010).
Electromagnetic radiation of energies 200 keV that derives from radioactive decay of a nucleus when it returns to a lower energetic state after a preceding alpha or beta decay. The operating distance in matter of density 2.5 g/ccm is about 30 cm.
Measurement of the discrete and isotope-specific gamma-emissions of the radioactive elements in a sample by means of a detector (semiconductor or mono-crystal). Via comparison to measurement results of a standard with known contents of radioelements and after conducting energy and efficiency calibration, activities and thus the concentration of U, Th and K of a sample can be determined. By comparing activities of distinct members of a decay chain, recently induced secular disequilibria may be detected with this method.
Emitted thermoluminescence signal from a sample recorded as a function of temperature. A glow curve is usually measured from room temperature up to 400 to 500 °C. For each type of sample (mineral), the glow curve contains specific peaks (intensity maxima), while the peak is the more stable the later it occurs in the glow curve. The position of individual peaks is dependent on the heating rate used (higher heating rates lead to higher peak temperatures). Prominent examples are the unstable 110 °C and the optically sensitive 325 °C TL peak in quartz.
Unit of absorbed radiation dose (1 Gy = 1 J/kg). An antiquated unit of dose is rad (1 rd = 0.01 Gy).
Growth curve (see also dose response curve)
Amount of luminescence recorded as a function of administered dose, also called <emdose response curve</em. For equivalent dose determination, the so obtained data points are usually fitted with linear, quadratic or exponentially saturating functions.
g-value (see fading factor)
The time after which only half of the initial quantity of a radioactive substance remains. In the naturally occurring decay chains half-lifes span the range from 300 ns (decay from 212Po to 208Pb) up to 14.1 Ga (decay from 232Th to 228Ra).
Assumption for dose rate calculation that the matter causing the radiation field extends infinitely to all directions. As far as the boundary to areas with differing features of prevailing radiation (strength, type) is located far away in comparison to the range of the radiation of concern (alpha, beta or gamma), this condition is fulfilled.
Measurement in the field under conditions most closely representing the undisturbed geometry before sample taking. For instance, dose rate measurements in complex and inhomogeneous environments carried out in-situ are more representative for the “true” dose rate experienced by the sample than laboratory measurements of homogenized sediment.
Dissociation of an electron from the electronic shell of an atom which is then called ion.
Incidence of ionizing radiation (alpha- and beta-particles, and gamma rays).
IR depletion ratio
Relation of the optically (blue, green) stimulated luminescence signal after IR bleaching to the OSL signal without prior IR bleaching, using the same regeneration dose. Within the frame of the SAR protocol, one regeneration point is repeated at the end of the sequence containing a preheat and a preceding IR bleaching step at 125 °C (to ensure identical measurement conditions as employed for regular OSL readout) (Mauz and Lang 2004).
IRSL (Infrared stimulated luminescence)
Method of inducing luminescence by exposing (stimulating) the sample to infrared light (usually at about 880nm). This approach is used for dating feldspars.
Subcategories of an element, each characterized by an identical number of protons in the nucleus (controlling the chemical properties), but different numbers of neutrons, and thus varying atomic masses. There are e.g. different isotopes of carbon (12C, 13C, 14C or 235U, 238U). Some isotopes are unstable and undergo radioactive decay, resulting in another isotope or element.
In terms of luminescence of solids, the kinetics stands for the rate equations describing the charge movement under certain assumptions. For instance, first-order kinetics disregards any retrapping of charge in traps after eviction, while second-order kinetics does. The kinetic order is often expressed in terms of the parameter b. There is also the possibility of mixed-order kinetics, e.g. b = 1.5.
The k-value, expressing the alpha-efficiency, is defined as the ratio of the luminescence induced per Gy of 3.7 MeV alpha particles and the luminescence induced per Gy of beta radiation (Zimmerman 1971). The need to use mono-energetic alpha particles arises from the energy dependence of this type of radiation in luminescence production. Therefore, 241Am is usually used whose particles have approximately 3.7 MeV after crossing the source’s protective layer. However, to adapt the k-value derived from laboratory irradiation (k3.7) to the natural spectrum of alpha radiation (0 to 8.8 MeV), keff must be calculated. For the U series keff/k3.7 = 0.80 and for the Th series keff/k3.7 = 0.86 (for equal activities of U and Th keff/k3.7 = 0.83) (Zimmerman 1971).
Average time an electron or hole is expected to spend in a trapped state. The lifetime t depends mainly on surrounding temperature T, trap depth (or activation energy) E and frequency factor s; it can be calculated by t = 1/s*exp(E/kT), with k being Boltzmann’s constant.
Mode of optical stimulation where the power of the stimulation is increased linearly from zero to a maximum value (Bulur 1996). The resulting LM-OSL decay curve shows – in contrast to the CW-OSL decay curve – one or more distinct peaks, facilitating a more intuitive assessment of quartz OSL signal composition. To obtain more detailed and quantitative information on photo-ionization cross-sections and defect concentrations of distinct signal components (trap types), the LM-OSL curve can be deconvolved by means of curve fitting.
Charge transfer from a trap to a recombination center without using the delocalized bands (conduction band for electrons, valence band for holes).
Light emission of a substance that is not related to blackbody radiation, i.e. to the temperature (‘cold light’). Luminescence can be caused by mechanical stress (triboluminescence), chemical reactions (chemiluminescence and bioluminescence) or irradiation.
Discrete state in the band gap that is attractive to positive charges (holes). If the center is activated (i.e., occupied by a hole) and an electron is captured to restore charge neutrality, luminescence is emitted when the captured electron relaxes from its excited state to the ground state. The color of emitted luminescence depends on the type of luminescence center. Common impurities in quartz that form luminescence centers are Al3+ or Ge3+.
Ratio of the luminescence signal resulting from the regeneration dose in the SAR protocol to the luminescence resulting from the constant test dose. This normalization procedure corrects for sensitivity changes, provided the measured test dose signal is a proxy of the sensitivity of the preceding regeneration measurement.
MAAD (Multiple aliquot additive protocol)
Protocol, in which each aliquot is measured only once (plus mostly a normalization measurement. Usually, the sample is divided into 4-8 portions consisting of ~2-6 aliquots each. These portions receive different additive doses, e.g., 0 Gy (natural luminescence), 50 Gy, 100 Gy, … The resulting luminescence is plotted against added doses and the dose points fitted with an adequate function (e.g., linear, single-saturating exponential, …) and the intersect of the extrapolated dose response curve with the dose axis gives the equivalent dose. This method works best in the linear part of the dose response curves (linear fit of dose points) and is advantageous for samples showing large and/or non-correctable sensitivity changes in regenerative-dose protocols. In case of coarse grain samples, a crucial point for the MAAD protocol is the normalization of dose points, as usually individual aliquots receiving the same additive dose show remarkable scatter in luminescence intensity (what in turn affects the precision of the obtained De).
The grain size fraction between ~38 µm and 63 µm (coarse silt).
Water in the pores of sediment or ceramics. As water absorbs ionizing radiation in a disproportionally strongly, assessment of the moisture content of sediments or ceramics is crucial for calculating a valid dose rate. Estimation of the moisture content over the whole burial period is difficult (e.g., due to climate changes or changes in the draining of a site) and one of the main limiting factors in increasing the precision of a luminescence age.
Procedure of eliminating the scatter of natural luminescence intensity between aliquots of a sample by referring to a common reference value (usually the average of all normalization measuremements). Each individual measurement result is thus multiplied by a normalization factor. Common normalization methods are short-shine measurements (OSL) or second-glow measurements after a fixed test dose (TL, OSL). Weight normalization is usually not successfull.
A dating method using OSL signal.
OSL (Optical stimulated luminescence)
Method of inducing luminescence by exposing (stimulating) the sample to visible light.
The dose accumulated during burial time. Due to the fact that the conditions of natural irradiation (spatial configuration, spectrum) cannot be reproduced in the laboratory and because the sensitivity of a sample is altered during the measurement, it cannot be determined directly. The equivalent dose is taken as an estimate of the palaeodose.
Local or global maximum of a TL glow curve, which represents the time or temperature when the rate of recombination (of electrons and holes) is highest. Each individual peak corresponds to a single trap type; however, single peaks may not be visible as those in the bulk glow curve due to overlapping. To separate them, TL glow curve deconvolution is necessary.
Change of peak temperature either with dose (kinetic peak shift) or between aliquots (thermal peak shift). The kinetic peak shift is regarded to originate from second-order kinetics, for which the peak temperature depends on the administered dose. The thermal peak shift is caused by different thermal conductivity of individual sample discs (different thermal lag).
Type of luminescence, for which the supply of external energy and the light emission are separated by a time gap of 10E-6 s up to several hours (Chen & McKeever 1997).
Emission of luminescence at the time of stimulation with light (=fluorescence); no previous supply of external energy is necessary (Yukihara & McKeever 2011).
Highly sensitive device for light detection up to the single-photon level.
Phototransferred thermoluminescence (PTTL)
Thermoluminescence resulting from charge that has previously been evicted from optically active traps (by optical stimulation) and retrapped in TL traps.
This term is usually used to describe the invariance of measurement or analyses results from measurement or analyses parameters. The plateau thus indicates a stable state of the system. For instance, the TL heating plateau marks the temperature region of the glow curve, for which the ratio of natural TL and natural TL + additive dose is constant, and thus the signal stable over the dating period. For construction of the De-plateau, various De-values are determined, but each for a small temperature region of the glow curve only (e.g., for 280-284 °C, 285-289 °C). Here, a range of constant De-values also indicates sufficient thermal stability of the signal in the plateau region.
Luminescence signal from feldspar resulting from elevated-temperature (e.g., 225 or 290 °C) IR stimulation after a first IR stimulation at 50 °C has been conducted. The post-IR IRSL (or pIRIR) signal is believed to be less prone to anomalous fading compared to the IRSL-50 signal.
precisionPrecision (see also accuracy)
This term describes the random (non-directed) errors related to a measurement. By repeating a measurement several times, the precision can be increased for statistical reasons (Wagner 1998; Geyh 2005).
Thermal treatment of a sample after artificial irradiation to achieve the same state of charge distribution as would have resulted from natural irradiation (low dose rate over prolonged periods). The main purpose is hence to empty shallow traps, which have filled during laboratory irradiation, but keep virtually empty in nature (e.g. the 110 °C TL trap).
Quartz inclusion technique
Applying this method, the coarse quartz grains are etched in HF for 40-80 min to remove the outer ~15-20 µm layer that has been exposed to external alpha radiation. This allows neglecting the alpha contribution to the dose rate completely.
Programming language based on the programming language S. The R-language was originally developed to solve statistical problems. In the meantime a huge number of different packages were added to serve all kinds of scietific questions.
Also Galbraith’s radial plot. Plot of the standardized estimates against the inverted standard error. On the semi-circle the real values are shown.
Propagation of electromagnetic waves or particles with high kinetic energy through matter or vacuum.
Amount of absorbed radiation energy per unit mass.
The SI unit is 1 Gy = 1 J/kg.
Spontaneous decay of unstable atomic nuclei by emission of ionizing radiation (alpha- and beta particles, and gamma rays).
Recombination center (see Luminescence center)
The recycling ratio is a test for the reproducibility of dose absorption. It is carried out by giving the same dose to two different dose-points, usually the first and the last one. The ratio of the two sensitivity-corrected signals should be 1. Within a range of 0.9 to 1.1, the recycling ratio is in an acceptable limit (Murray and Wintle 2000). This test indicates, whether the SAR protocol and the sensitivity-correction are adequate for measurement.
SAR (Single aliquot regeneration protocol)
SARA (Single-aliquot regeneration and added dose protocol)
A sample is regarded as saturated when it can not store any more energy in its crystal lattice, that means all traps are filled. For the dating process it is only possible to point out a minnimum age.
Self-dosing (See also auto-regeneration)
Contribution to the dose rate coming from inside the dated mineral fraction (also called self-irradiation or internal dose rate). In contrast to most quartz samples, where self-dosing is negligible, feldspar (due to K-concentrations of 12.5 ± 0.5 wt.%; Huntley & Baril 1997) and silex samples, e.g., may show considerable internal dose rates. The advantage of a (high) internal dose rate is its continuity over burial time, unlike the environmental dose rate, being prone to temporal fluctuations. However, if internal radioelements (especially U and Th, as often observed in silex) are non-uniformly distributed, microdosimetric effects my lead to systematic errors (Schmidt et al. 2012).
Luminescence response to unity dose. The sensitivity may vary from sample to sample and increase or decrease in the course of thermal and optical treatments and irradiation (e.g. also in the course of the luminescence measurement procedure). In luminescence modelling, irradiation and thermally induced sensitivity changes are often associated with the activation of so-called reservoirs centers that compete for holes with recombination centers during irradiation (Li 2001; Bailey 2001). To correct for varying sensitivity among different aliquots and for changing sensitivity during measurement cycles, normalization procedures are applied (see Normalization).
Shine down curve
Luminescence of longer wavelength than the stimulation wavelength.
Fixed dose which is delivered to an aliquot and the resulting luminescence measured for the purpose of normalization or sensitivity correction (e.g. in the SAR protocol after each regeneration cycle; Murray & Wintle 2000). The test dose should be chosen as small as possible to avoid dose effects.
Effect in thermal stimulation describing the difference of the actual sample temperature (temperature of the mineral grains) and the “should-be” temperature (i.e. either that given by the software or that measured, mostly in the heating plate). It can be caused by poor mechanical contact between disc/cup and heater plate, low heat conductance of the disc/cup material and the thickness of the discs/cups. The absolute amount of thermal lag can be reduced by using low heating rates. Thermal lag leads to TL peak shift towards higher temperatures.
Position in the crystal lattice which is not occupied by an atom and thus classified as intrinsic point defect. These defects are present in all real and even ideal crystals above 0 K and act as charge trap. For instance, prominent vacancies are missing O atoms in quartz, causing a positive net charge and hence being capable of trapping an electron to achieve charge compensation (Preusser et al. 2009).
Energetic level in the energy band model in which electrons are bound to their host atoms. Defect electrons (holes), however, are able to migrate through the conduction band as electrons are passed from one atom to another so that the hole moves in the opposite direction. In the ground state of insulators, the valence band is filled with electrons while the conduction band is empty.
Distance between two troughs or crests of an electromagnetic wave.
Electromagnetic radiation in the energy range between ca. 100 eV (wavelength of 10 nm) and several MeV (wavelength of 1 pm).
The erasure of the absorbed dose of a sample by heating (annealing) or illumination (bleaching, of the light-sensitive signal components only).