Electron Spin Resonance Dating, or ESR dating, is a technique used to date newly formed materials, which Radiocarbon dating cannot, like carbonates, tooth . Indeed, for Electron Spin Resonance (ESR) dating of tooth enamel, the origin of the sample as well as its 3Electron Spin Resonance can be used to date fossil teeth with an age ranging from around 2 Ma to 30 ka . Table des illustrations. Electron paramagnetic resonance response of fossil tooth enamel to ionizing Table. Page. 1. Radionuclide activity concentrations (pCi/g) in tooth enamel and (EPR, also known as electron spin resonance or ESR) dating of tooth enamel.
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.
Radiometric analysis is widely used for determining natural radioisotopes in geological samples by means of spectroscopic methods and, especially, for quantifying the uranium, thorium and potassium present in samples. A linear model was used for fitting ESR signal intensity to dose, as has been done by other authors Baffa et al.
ROSY software Brennan et al. Soil water content was The software's default values were used for the remaining parameters. Finding the dose rate to convert DA into an age is a crucial step after DA has been found. ROSY software allows age to be calculated from an enamel sample by taking DA due to radioisotopes from adjacent layers into account. The software computes age based on three uranium absorption models linear, early uptake and a combination of both.
Electron spin resonance dating - Wikipedia
Table 1 shows the soil analysis results. The present work did not determine U, Th and K concentration in enamel and dentine as their percentages have been negligible for calculating age in previous work, especially in dates for the Holocene period Kinoshita et al. Typical soil density, enamel and dentine values were used for calculating age 2.
Using these values and the radioisotope concentrations listed in Table 1ROSY software was used for obtaining the alpha, beta and gamma radiation dose rate contribution for each radioisotope in sediment the results are listed in Table 2.
These results were the same for any uranium absorption model. It should be noted that ROSY software calculates these ages using three uranium accumulation models: The way that uranium accumulates in a tooth is established by these models; accumulation increases at the same rate as time in the linear model and accumulation occurs in a short period of time in the early model, relative to a tooth's age and then remains constant after this short period of time.
The tooth's age was the same when calculated by these three methods; this result was consistent if taken into account that the accumulation of radioactive elements inside the tooth was negligible. Conclusions Age determined at many countries' archaeological sites is the result of radiocarbon 14C analysis of particular items found around the burials and not direct dating of individuals found there. The results regarding either physical or geological phenomena may not be chronologically equal, hence the importance of having techniques like ESR which can directly and absolutely determine the age of individuals of interest.
This numerical dating method is based on the study of the radioactive decay of 14 C in organisms after their death and may provide accurate ages for samples containing organic matter like fossil bones or charcoals. 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.
Quaternary dating by electron spin resonance (ESR) applied to human tooth enamel
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. 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.Benefits of Benchtop Electron Spin Resonance
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.
Dating fossil teeth by electron paramagnetic resonance: how is that possible?
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.
Dating Conodonts Using Electron Spin Resonance: A Possible Technique
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.
For the evaluation of the cosmic dose rate, it is necessary to get an estimation of the thickness of the overlying deposits. Sometimes, the actual situation is not representative of the past history, especially if erosion took place and removed most of the sediment cover.
In this case, the maximum sediment thickness above the sample should be estimated as well. Nevertheless, as far as possible, the gamma dose rate should always be derived from in situ measurements. Sometimes, fossil teeth are taken from collections and their exact original location spot may no longer exist. Consequently, in situ measurements have to be performed as closely as possible to the tooth original position.
- Electron spin resonance dating
Indeed, a tooth cannot be dated without a good knowledge of its sedimentary context, since the dose rate needs to be accurately reconstructed. By definition, field work is the first step of the ESR dating procedure, and the reliability of the age result depends on the accuracy of the data collected on site, such as the position of the tooth and its embedding sediment, the in situ dosimetry measurements and the estimation of the thickness of the overlying deposits.
In order to implement ESR dating under the best possible conditions, we provided here some guidelines and designed a sampling form for non-ESR specialists intending to sample teeth, as it includes all the data necessary to record and report for an ESR age calculation. The tooth and sediment sampling can be easily performed by following the basic instructions given above and should be carried out while the excavation is still ongoing.