E-mail: [ protected]. Electron paramagnetic resonance EPR spectroscopy is a powerful and versatile technique that is frequently used for quantitative and qualitative analysis in a wide range of scientific fields such as chemistryphysics, biology, medicine, geology and archaeology.
Unlike radiometric methods based on the measurement of radioactive growth or decay of isotopes e.
We used DosiVox to evaluate the impact of cement thickness on the dose effectively absorbed by the enamel layer. Instead, if adjacent tissues are present, their thickness is by default assumed to be sufficient to fulfill the infinite matrix conditions. One of the main difficulties in Electron Spin Resonance ESR dating of fossil teeth lies in the complexity of the system that has to be considered for dose rate evaluation.
Uranium and Thorium in the Constituents of Fossil Teeth. Dating fossil teeth TL 14 1 : 21— Densities of modern and fossil dental tissues: ificance to ESR dating of tooth enamel. Ancient TL 15 2—3 : 20— If the initial and removed thickness of the enamel layer is usually taken into consideration for Dating fossil teeth alpha and beta dose rate attenuation and self-absorption factors, the thickness of the adjacent tissues dentine, cement is in contrast very rarely considered in the dose rate evaluation. Quaternary Geochronology 4 3 : —, DOI Quaternary Geochronology 99—, DOI In order to evaluate to which extent this assumption is correct and how it may impact the external beta dose rate absorbed by the enamel layer, we used DosiVox, a Geant4-based software simulating the interactions of particles within a material for dosimetric purposes Martin L, Incerti S and Mercier N, a.
DosiVox: Implementing Geant 4-based software for dosimetry simulations relevant to luminescence and ESR dating techniques. Ancient TL 33 1 : 1— With this software, it Dating fossil teeth now possible to model more complex geometries like fossil teeth, and we performed several simulations with an outer tissue thickness varying between 0 and 2 mm.
are presented and discussed hereafter. A tooth is typically made of several tissues mostly dentine, enamel and cement that differ in many aspects such as chemical composition, mineralization, density or thickness see overviews in Driessens FC, The mineral in bone, dentin and tooth enamel.
Calcium Phosphate Biominerals. Cambridge University Press. Tooth structure and geometry is highly variable depending on the type and species considered Hillson S, For example, enamel is the outermost layer in human tooth crown, which means that it is in direct contact with the Dating fossil teeth on its external side.
In contrast, fossil equid teeth are notoriously famous for having cement capping the external side of the enamel layer. As a consequence, the sediment is not in direct contact with the enamel.
Basically, these two situations have different implications in terms Dating fossil teeth dose rate evaluation, and especially for the alpha and beta components. In ESR dating, teeth are typically approximated to a succession of thin layers. Two main geometries can usually be considered, depending on whether the enamel layer is on one side in direct contact with the sediment:. This tissue is usually cement e. The challenge of dating Early Pleistocene fossil teeth by the combined uranium series—electron spin resonance method: the Venta Micena palaeontological site Orce, Spain. Uranium accumulation in teeth and its effect on ESR dating — A detailed study of a mammoth tooth.
Geometry 1 is illustrated in Fig. Radiation Measurements 27 5—6 : —, DOI Encyclopedia of Scientific Dating fossil teeth Methods. Rink and J. Thompson, Springer Netherlands: pp — Thompson J. Shown here is the cement-enamel-dentine geometry. In blue italics, the radioactive sources present in each material dental tissues and sediment.
Dose rate evaluation in fossil teeth is usually based on a series of considerations that may be summarized as follows:.
Dating fossil teeth by electron paramagnetic resonance: how is that possible?
Suggestions for minimum requirements for reporting ESR age estimates. Ancient TL 10 3 : 37— Both the gamma dose rate from the dental tissues and the gamma attenuation by the tooth are considered negligible, unless the tooth is ificantly bigger than usual e. Open system modelling for U-series and ESR dating of teeth.
Consequently, the alpha and beta dose rate components in dental tissues come from the U decay chain alone. In contrast, because the standard penetration depth of the beta particles about 2 mm is in the same order of magnitude of the usual thickness of dental tissues typically around 1.
Instead, the Dating fossil teeth of the beta particles has to be considered, together with the thickness of the enamel layer removed on both sides. A succession of thin and homogeneous layers is considered for the external beta dose rate evaluation. Nuclear Tracks and Radiation Measurements 14 1—2 : — Further details about this approach may be found in Duval M, They, however, do not take into consideration the thickness of the tissues adjacent to the enamel layer in the beta dose rate evaluation.
Consequently, the choice of either option 1 or 2 may have a non-negligible impact on the calculated age, depending on whether dental tissues carry a ificant weight in the total dose rate. This briefly illustrates the potential impact of the tooth geometry considered for the sample that is being dated. However, this assumption may sometimes be wrong.
For example, the thickness of the cement layer in equid teeth is known to be highly variable depending on the type of tooth, the age at the death of the animal, as well as longitudinally, from the occlusal surface to the roots e. Burke A and Castanet J, Dating fossil teeth However, it is simply unknown in which extent it may impact the final age result.
Considering a thickness that fulfills the infinite matrix conditions would lead to the calculation of an overestimated beta dose rate value and thus an underestimated US-ESR Dating fossil teeth if the tissue thickness is thinner than 2 mm. In contrast, considering no dental tissue on the outer side of the enamel layer would underestimate the true beta dose rate and yield thus an overestimated US-ESR age. In first instance, the true age of the sample would be located somewhere in between those two calculations.
However, this evaluation cannot be considered as fully satisfactory given the magnitude of the uncertainty involved see example above with sample B. The mean path length of electrons emitted by these elements depends on the environment considered, and is influenced by different parameters such as water content and chemical composition of the materials. Beta attenuation in thin layers. Ancient TL 4: 1—8.
Tables of beta-ray dose distributions in water. Radiation Measurements 27 2 : —, DOI Comparison of DosiVox simulation with tabulated data and standard calculations. Ancient TL 33 2 : 1—9. In our case, it offers the possibility to properly evaluate in which extent the presence of an outer dental Dating fossil teeth with variable thickness may impact the external beta dose rate.
Five different simulations were performed using a cement thickness varying between 0 and 2 mm. Beta dose rate modelling was carried out with DosiVox program version 1.
Dose-rate conversion factors: update. Ancient TL 29 1 : 5—8. Budapest, Hungary, October With DosiVox, simulations are performed in a three dimensional 3D grid divided in a series of voxels whose resolution and size may differ along the three axis see details in Martin L, Incerti S and Mercier N, a.
In our study, sample geometry was approximated to the stratified-sediment case presented in Martin L, Incerti S and Mercier N, a. Dating fossil teeth, a 3D rectangular parallelepiped of variable length z axis was deed, with a resolution of 0. Five cases were considered for simulation, with different cement thicknesses: 2 mm case 11 mm case 20. A cylindrical probe was selected among the range of detectors available in DosiVox, with a diameter set to 3 mm.
The 3D models generated for the simulations are displayed in Supplementary material, Figure S1. The of voxels used for each component along the z-axis is indicated in the red boxes. Simulations were performed by considering 10, 20 and 30 pm of U in the cement. In comparison, uranium concentration in the enamel, dentine and cement was assumed to be of 1, 50 and 10—30 ppm.
The characteristics of each material chemical composition, density, water content used in the simulations are provided in Supplementary material, Table S1. In order to avoid too complex simulations and obtain that can be directly compared with those from DATA and USESR programs, a couple of assumptions were considered:. Equilibrium in the U decay chain for both dental tissues and sediment was assumed.
We are aware that this assumption is most likely incorrect for Dating fossil teeth tissues, but DosiVox does not presently contemplate U-series disequilibrium.