Quaternary dating by electron spin resonance (ESR) applied to human tooth . However, no significant difference in the accuracy of dose reconstruction has yet Radiometric analysis is widely used for determining natural radioisotopes in. electron spin resonance (ESR) dating of tooth enamel, which, together with the related obtained so far for fossil hominid sites relevant to the origin of modern The importance of accurate dating to the resolution of the present dispute about. I would consider electron spin resonance to be more accurate as in carbon dating method it can be giving wrong dating due to natural activities.
Quaternary dating by electron spin resonance (ESR) applied to human tooth enamel
Radiocarbon is usually classified as a radiometric dating method, which corresponds to a group of techniques based on the measurement of the radioactive decay or production of specific radioelements e.
But there is also another group of dating approaches that are based instead on the evaluation of the effects of natural radioactivity on some materials over time, which are quantified in terms of the radiation dose absorbed i.
These are usually called palaeodosimetric or trapped charge dating methods, mainly based either on the study of radiation-induced luminescence, e. The first application of EPR for a dating purpose was carried out during the mids on a stalagmite from a Japanese cave, 1 about 30 years after the discovery of EPR by E. Since then, numerous dating applications have been developed on many different materials such as silicates e.
A quite complete overview may be found in Reference 2.
The first studies on fossil bones were published in the early s, however, these were then naturally oriented towards the teeth, since enamel was rapidly found to have more suitable characteristics for dating.
Since then, the method has progressively gained in accuracy over the following decades, especially via a better understanding of the EPR signal of fossil enamel and of its behaviour with the absorbed dose, as well as of the modelling of uranium uptake into dental tissues.
The objective of this article is to explain how EPR may be converted into a dating tool for fossil teeth. These may be either naturally present in some materials, or created by physical or chemical reactions.
With regard to the latter, some materials can acquire paramagnetic properties under the effect of radioactivity. The interaction of ionising radiations with the matter may induce modifications of the electronic structure of some materials: These species create a signal that can be detected by EPR spectroscopy, the intensity of which is directly dependent on the amount of trapped charges in the crystalline network, reflecting thus the dose absorbed by the material.
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EPR spectroscopy is now widely recognised as a reference technique for routine dosimetry by many international institutions [e. Over the last decades, many applications have been developed, including those for post-accident dose reconstruction in the environment, biophysical dosimetry using human tissues, to identify irradiated foods, and some of them, such as the alanine dosimetry, have reached a high-level of standardisation. Hydroxyapatite, the main component of bones and teeth, is especially sensitive to ionising radiation: It is now internationally accepted as a valuable natural EPR dosimeter, and is commonly used in the field of retrospective dosimetry for persons accidentally exposed to ionising radiation.
An extensive review on this aspect may be found in Reference 4. From a mineralogical point of view, tooth enamel is mainly made of carbonated hydroxyapatite [Ca10 PO4 6 OH 2] like dentine or bones. These characteristics make tooth enamel especially stable over time, i. The EPR signal associated with fossil hydroxyapatite is an asymmetric composite signal. The main radiation-induced signal is defined by three peaks T1, B1 and B2, see Figure 1.
Many contributions to this signal have been identified, mainly carbonate-derived radicals and some oxygen radicals, 4 but the major contribution comes from three kinds of CO2— radicals, whose precursors are very likely the carbonate groups CO32— present in the hydroxyapatite. This natural radioactivity is due to the radioelements, mainly U-series, Th-series and 40K elementsthat are not only naturally present in the sediment, but are also progressively incorporated into the dental tissues.
Ionising radiations emitted by these radioelements are alpha and beta particles as well as gamma rays Figure 1. Together with cosmic rays, they contribute to build up a dose in the enamel over time, the magnitude of which will mainly depend on two main parameters: This relationship may be converted into an EPR age equation as follows: This work is carried out in two different ways: To obtain an accurate evaluation of the total dose rate, it is important to divide it into several components.
Electron spin resonance dating - Wikipedia
The specificity of teeth dating relies on the complex system that has to be considered, because a tooth is usually made by several tissues enamel, dentine and, sometimes, cement; Figure 2having various thicknesses and composition. Moreover, isochronal experiment revealed that the gouge did not comprise pure carbonates but consisted of a mixture of calcite and quartz grains. A younger age value would have been obtained if a lower artificial irradiation dose rate and a relatively pure carbonate fault gouge were used in the ED determination.
Introduction Active tectonics is associated with uplifts, earthquakes, volcanic eruptions, landslides and faulting, which have been reported having a direct impact on the environment and population [ 12 ]. One of the countries in the World that is most vulnerable to the aforementioned components of active tectonics is Japan [ 34 ]. The environmental and human impacts from the incidence of active tectonics can among others be exemplified by the March 11, earthquake and tsunami along the northeastern coast of Japan, and the Niigata Chuetsu-Oki earthquakes.
These underscore the importance of monitoring of active tectonics. In recognition of this importance, earth scientists have not only intensified but also refined on both spatial and temporal dimensions the characterization of faults and earthquake prone zones in Japan.
As far as temporal characterization is concerned, quartz in fault gouges has been used to estimate the age of latest fault movements using the electron spin resonance ESR method [ 5 — 8 ].
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ESR has been used for dating the formation and more recent re-crystallisation of three types of gypsum samples: Other papers dating stalagmites, calcite, mollusc shells and reefs are Renfrew et al. The present study was aimed at using the ESR method for dating tooth enamel from the Aguazuque archaeological site in Soacha, Colombia. The human tooth used in this work was extracted from a skeleton labelled AG-I taken from a collective burial site where 23 people were found arranged in a foetal position; men, women and children were identified.
The burial site was circular shaped 4. Archaeological research concerning the early and middle Holocene period has led tore constructing the way of life for human groups in the region, thereby showing a transition from hunters and gatherers to agricultural societies Groot Electron spin resonance ESR consists of the resonant absorption of electromagnetic energy during electron-spin transitions. A static magnetic field should be applied to resolve different electron-spin levels.
Unpaired electrons from free radicals have spin equal to V. An important conclusion derived from this formula is the linear dependence between the applied magnetic field and resonance frequency. The most frequently used microwave energies drop in what is called the X band.
ESR dating and dosimetry are based on the fact that ionising radiation produces paramagnetic centres having long lifetimes in a number of materials.
Such centres' concentration in a given sample is a measure of the total radiation dose to which a particular sample has been exposed. This effect can be used to determine the length of time of such exposure and hence, in many cases, a sample's burial time Jonas The aim is to determine the accumulated dose DA to which a sample has been exposed whilst being buried; the exposure time is then determined by comparing DA to the average dose rate over such period: However, no significant difference in the accuracy of dose reconstruction has yet been found using different calibration methods Wieser et al.
Each sample's radiation sensitivity is individually calibrated for dose assessment by the additive dose method; each sample is incrementally irradiated with at least 14 additional doses up to Gy or more avoiding the sample becoming saturated.
A linear regression analysis is applied to the ESR measurements at each dose increment and the original measurement laboratory-un-irradiated sample. The original DA in the sample is obtained from the negative intercept of the regression line with the dose axis; is estimated as being the total radiation provided by all radioactive elements present in a sample and soil and also cosmic radiation Ikeya ; Jonas ; Walker ; Grun Materials and Methods The dentine was initially removed from teeth using a dental drill and water cooling.
The molar enamel powder was divided into nine aliquots. The spectrometer parameters used were: Soil samples were also collected from the Aguazuque site and sent for U, Th and K content analysis by gamma spectrometry.