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Although the basic principle of TL-dating is simple, the underlying assumptions are not trivial. One major source of error is the external dose rate, which contributes to a varying degree to the denominator of the age formula and thus has a varying influence on the dating result. The intention of this paper is to enable the user to evaluate TL age determinations of heated flint.

The parameters used for age determination and some of their relationships are discussed. It is shown that the reliability of TL results of heated flint depends on the proportion of the various dose-rate parameters and that these are important for the evaluation of ages.

The limitations of the method as well as the advantages are discussed. The application ranges from Lower Paleolithic to Neolithic archaeological sites, with a major focus on the Middle Paleolithic, which is often beyond the range of the 14C-dating method. The application of TL dating on heated flint is mainly limited by the detection limits of the equipment for very young samples, the saturation of the signal measured for very old samples, and, of course, the presence of sufficiently burnt flint.

It is thus, in principle, possible to date fire use over the entire human evolution. Recent reviews of luminescence dating in archaeology can be found in Roberts and Wagner The advantages and disadvantages of TL dating of heated flint will be discussed here and special emphasis is put on potential problems and the underlying assump- tions.

This discussion omits the fundamental physics of the method and concentrates more on the application of this dating method. An International Journal, Vol. Published online in Wiley Interscience www. In contrast to many other chronometric dating methods, it is thus possible to directly date a past human activity. Naturally occurring fires are unlikely to be responsible for heating in most Paleolithic sites see also Alperson-Afil et al. Therefore, only a sum- mary and a simple description of the principles are given here, with an emphasis on the issues relevant for users and for the evaluation of luminescence ages.

Luminescence dating is based on structural damage and faults to the crystal lattice of minerals by ionizing radiation. The sources for this omnipresent radiation are radioactive nuclides from the surrounding sediment and from the sample itself, as well as secondary cosmic rays. The paleodose is proportional to the dose rate D , which is the ionizing radiation per time unit at the position of the sample within the sediment.

This dose rate provides the clock for the dating application. Exposure to light or temperature causes the electrons to relax to a ground state, sometimes by emitting a photon, the lumines- cence. The intensity of the luminescence signal number of photons increases with the total absorbed dose P in a crystal and is therefore a function of exposure time to radiation. This accumulation starts with the formation of the mineral. But in most geoar- chaeological applications, the interest lies in the time elapsed since human activity e.

Therefore, the mineral had to be either heated or exposed to light at the time of interest in antiquity. After deposition and protection from light, a radiation dose, and thus a latent luminescence signal, accumulates again until it is measured in the laboratory Figure 1. Latent luminescence signal since mineral formation until it is zeroed by exposure to heat or light in antiquity.

After burial, the luminescence signal accumulates again and the sample is measured in the laboratory. The numerator and denominator of this formula consist of several parameters, each of which will be discussed in more detail.

This pale- odose is determined from the TL signal, which is measured by heating sample aliquots at a constant rate, producing the glow curves Figure 2a and 2c. Three different types of glow curves have to be distinguished: The goal is to construct and reconstruct the growth of the luminescence signal with increasing radiation doses Figure 2aâ€”c.

The resulting dose growth curves Figure 2b are measures of the sensitivity of a sample to ionizing radiation, consisting of several dose points, and are used to determine the paleodose.

There are essentially two ways to determine P in TL dating of heated flint Figure 2b. They differ in the way the paleodose is determined. The standard method Aitken, performs regression analyses for both growth curves and the sum of their absolute values essentially provide, P P1 in Figure 2b.

Glow curves and growth curves used in TL dating: In Figure 2b, the deter- mination of the paleodose P is shown, where P1 is the sum of the regression analysis of the additive and the regeneration dose curves standard method ; P2 is determined by shifting one dose curve toward the other normalization method ; and P3 is matching the NTL signal arrows to the regeneration dose curve SAR method. The first method can be applied only to younger samples whose dose points are still in the quasi-linear region of the growth curve, whereas the second method is used for older samples that are at the onset of saturation of the TL signal.

In this method a single-aliquot-regeneration SAR protocol with only two regeneration points Figure 2c is used. This method is especially useful for samples too small for the other methods, as it requires little material for analysis.

But the two established methods described earlier are the methods of choice, at least until this new approach has been shown to be generally applicable to a wider variety of different materials. Nevertheless, it seems to have potential and opens the possibility of dating more Paleolithic sites, pre- viously considered not to be datable by TL on heated flint. Common to all three approaches is the necessity to measure the effectiveness of alpha radiation, which has to be determined for each individual sample due to the high variability in sensitivity of flint samples.

Heating and Bleaching Before performing a full dating analysis, each sample must be checked to determine whether the heating in antiquity was sufficiently high for dating purposes. Samples are selected according to macroscopic signs reddish or pink color, glossy scars or glossy [luster] surface, crazing, pot lids, or cracked faces that indicate heating e. The sufficiency ca. Additionally, the shape and temperature of the glow peak can provide evidence of sufficiency of ancient heat- ing e.

Exposure to light can have a similar zeroing bleaching effect. Although there is little evidence of sensitivity to bleaching of the high-temperature TL peak used in dat- ing heated flint Huxtable and Aitken, ; Valladas, a , care has to be taken with translucent samples, which might have been bleached during or after excavation. Such bleaching would give rise to severe age underestimation.

It is, therefore, necessary in some cases to check whether the TL-peak used is prone to bleaching e. It is advisable not to expose potential samples to direct sun- light, and, as a precaution, samples should be wrapped in aluminium foil soon after discovery. Obviously, the denominator is crucial for the accurate determination of an age. Nevertheless, it is sometimes necessary to model D. These issues will be discussed below. The Dinternal thus is considered as being constant over the time span of interest in archaeological dating.

The Dinternal dose rates for each sample are calculated from the element concentrations Adamiec and Aitken, , which are usually determined by neutron activation analysis NAA from the crushed unprepared sample. Fission track analysis has shown the presence of hot spots of radioactive elements in a few samples Valladas, b. But due to crushing, the sample is homogenized, and it is assumed that any inhomogeneity of radioactive element distribution is thus negligible Valladas, b.

External dose rate Sediment contains not only the flint samples, but radioactive nuclides as well. Although the latter have penetration depths in rock or sediment of up to several tens of meters, the range for the ionizing radiation from the radioactive nuclides is much smaller. This is of special concern because this dose rate has to be measured in the field, e. This dose rate may vary to some degree within a sedimentological unit throughout a site e.

Especially in caves in limestone regions, areas with large rocks tend to have a lower dose rate than areas where fine-grained material dominates the composi- tion of the sediment Figure 3. As the measurement cannot be performed at the exact location of each sample for obvious reasons , any modeling after excavation is not only tedious but also prone to error. Nevertheless, modeling might be neces- sary if all sediments have been removed e.

It is advisable to Figure 3. This leads to high dose rate, homogeneous radiation fields or low dose rate, lumpy radiation environments. Furthermore, it can be reoccurring. Therefore, site formation processes and post-depositional disturbances should be taken into account. Its proportional contribution to the total dose rate determines the effect of any variation in the dose-rate modeling. TL dating of heated flint can be almost independent from the external dose rate and DOI: Note that zero cosmic dose is assumed here for ease of comparison.

The precision and accuracy of thermoluminescence dating results are highly dependent on these proportions e.

Four sedimento- logical units of silt and clay have been differentiated on the basis of their colors. The archaeological remains are independent of these units, as they consist of an 80 cm thick deposit made up almost entirely of flint artifacts with little fine-grained material in between. Sedimentological analysis revealed the presence of fluvial and slope wash sediments, but no correlation was found with the units.

Although no vertical or hor- izontal sorting was observed, a distinct spatial distribution of certain artifact types over the 45 m2 excavated area was found Marks, Note that Dexternal includes a small cosmic dose that could be considered as stable as well after Rink et al. Thermoluminescence dating was performed on five samples of heated flint Rink et al.

The spread of the resulting ages is enormous, ranging from 14 to 48 ka Table II. As the other samples do not seem to have received similar Dexternal it must be suspected that these samples do not belong to a common heating event either. Heating at different times would have resulted in dif- ferent doses.

Given the depositional environment, it is quite possible that deflation occurred, which would make several independent heating events possible. These could have been different occupations with the samples related to these events. Equally possible are later heating events, where the actual deposition of a sample is unrelated to the heating. Additionally, near-surface or exposed artifacts could have been heated more than once.

This could have led to repeated full or partial zeroing, which is not distinguishable by standard TL-dating measurements. Furthermore, surface exposure could have led to a heating of the samples by the sun. The resulting average temperature over the burial history thus would have been much higher than generally assumed for well-buried samples.

This leads to a much reduced time of residence of the exited electrons, commonly referred to as lifetime for a TL peak of a certain temperature. Sun bleaching of the TL signal used for dating is generally not considered to be a problem for such dark flint, but it cannot be entirely ruled out because of the high variability of the flint material in general.

Signal bleaching and heating both caused by surface exposure therefore could be responsible for some DOI: Obviously the results do not belong to one statistical group. Due to the suspected reheating, all TL ages were discarded in the final analysis of the age of the site Rink et al. There are typological and techno- logical indications of the presence of Middle as well as Upper Paleolithic elements.

These layers at Um el Tlell have been dated to

Analecta Praehistoria Leidensia, 18, 41â€” Although the basic principle of TL-dating is simple, the underlying assumptions **Dating berlin online stream** not trivial. Huxtable, *Dating berlin online stream*, J. I am also indebted to the two anonymous reviewers, whose comments and suggestions considerably improved the paper. Equally possible are later heating events, where the actual deposition of a sample is unrelated to the heating. Hitler escaped Berlin bunker and died in South America, new book claims. Warke, P. It is, therefore, necessary in some cases to check whether the TL-peak used is prone to bleaching e. Additionally, the shape and temperature of the glow peak can provide evidence of sufficiency of ancient heat- ing e. This leads to a much reduced time of residence of the exited electrons, commonly referred to as lifetime for a TL peak of a certain temperature.