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Using artificially created swift, heavy ions of 129I with a typical fission-fragment mass and specific energies which are common during the spontaneous fission of 238U, the response in minerals commonly used in geochronological dating such as muscovite, zircon and apatite, has been evaluated by the means of Atomic Force Microscopy (AFM). The surface impact structures form hillocks with greater diameters but smaller heights for low-energetic ions and smaller diameters but greater heights for high-energetic ions. The observed hillock widths range from 22 ± 2 nm for low-energetic ions to 17 ± 1 nm for the highest energy in mica. Furthermore, the dimensions formed in apatite for low and high-energy ions range from 53 ± 2 nm to 27 ± 2 nm and from 64 ± 3 nm to 28 ± 1 nm in zircon. With increasing 129I particle energy hillock heights increase, but diameters decrease regardless of mineral orientation. The crystallographic orientation of apatite and zircon also seems to have no effect on hillock dimensions, which are identical for perpendicular and parallel to the c-axis oriented mineral grains. The results support the “Compound Spike” track formation model of Chadderton (2003), which combines the Coulomb ion explosion model with a thermal spike model. [ABSTRACT FROM AUTHOR]

Abstract: One of the purposes of this study is to give further constraints on the temperature range of the zircon partial annealing zone over a geological time scale using data from borehole zircon samples, which have experienced stable temperatures for ∼1 Ma. In this way, the extrapolation problem is explicitly addressed by fitting the zircon annealing models with geological timescale data. Several empirical model formulations have been proposed to perform these calibrations and have been compared in this work. The basic form proposed for annealing models is the Arrhenius-type model. There are other annealing models, that are based on the same general formulation. These empirical model equations have been preferred due to the great number of phenomena from track formation to chemical etching that are not well understood. However, there are two other models, which try to establish a direct correlation between their parameters and the related phenomena. To compare the response of the different annealing models, thermal indexes, such as closure temperature, total annealing temperature and the partial annealing zone, have been calculated and compared with field evidence. After comparing the different models, it was concluded that the fanning curvilinear models yield the best agreement between predicted index temperatures and field evidence. [Copyright &y& Elsevier]

Abstract: Thermoluminescence (TL), which is commonly used to date burnt flints from Palaeolithic sites, sometimes yields ages which are younger than those obtained by other methods. Many reasons could explain such discrepancies and one concerns the evaluation of the dose-rate originating from the sample itself, i.e., the internal dose-rate. In order to refine the parameters used in the internal dose-rate estimation, we investigated the uranium (U) distribution by the induced fission track method in three archaeological flint specimens. This approach shows that the U distribution is roughly uniform on a scale of a millimetre but not on a smaller scale (<100μm), because of the presence of quartz grains whose size is sample-dependent and because of relatively high local U concentrations. Therefore, the assumption of a homogeneous U distribution currently used to estimate the beta and alpha dose-rates may not be fully appropriate for all samples; in this case, this could lead to an underestimate of the TL age. [Copyright &y& Elsevier]

Abstract: Combined ESR/U-series dating of tooth enamel is important for obtaining chronological constraints on archaeological sites. The precision and accuracy of this method depend on the uncertainties associated with the equivalent dose and the dose rate. The precision of the dose rate calculation, in turn, depends on a number of parameters such as the internal radionuclide concentrations and distributions in the enamel, dentine and cementum and in the surrounding sediments as well as on the cosmogenic dose rate. Furthermore, teeth are open systems for U and therefore constraints on the U-uptake model are needed. The combination of all the uncertainties results in uncertainties of on the age at 95% confidence level. This can, however, be improved by reducing the uncertainties on the internal radionuclide concentrations and distributions. We present a comparison of three methods for measuring the U concentrations in dental tissue of a 40ka old equid tooth. Fission tracks are used to map the U distribution with high spatial resolution. The U and Th concentrations and isotopic compositions were measured with high precision but poor spatial resolution using TIMS. It is demonstrated that in situ LA-ICPMS provides an effective method for precise measurements of the U concentration at high spatial resolution. This method also has high potential for isotopic U-series measurements using MC-ICPMS. The results of the U measurements are used to constrain the effective alpha- and beta-dose rates in enamel sampled for ESR analysis. The TIMS U–Th isotope concentrations and in particular the 230Th concentrations are used to constrain the U uptake for combined ESR/U-series dating. [Copyright &y& Elsevier]

Abstract: A model for the annealing kinetics of fission tracks is proposed based on a simplified track. The principal hypothesis is that the atoms displaced during the passage of the fission fragment have to transmit through a potential barrier to occupy the vacant sites left. The resulting model equation is applied to zircon data both from laboratory and geological sources. The model succeeded in fitting the data and the addition of the geological data during the fitting procedure improved the extrapolation of the model to the timescale of millions of years, which is the timescale of interest in geology applications. [Copyright &y& Elsevier]

Abstract: Fission tracks in glass samples are shortened when they experience thermal treatment. Consequently, the observable dimensions associated with track length also diminish. The dimension normally used to characterize track size is the mean diameter of the etched track at the surface, D. Another consequence of length shortening is the reduction of surface density, , implying a reduction of the fission-track age. In this work, a kinetic model is developed to describe the relationship between fission-track mean diameter shortening and surface fission-track density reduction in glass samples, based on geometrical and etching hypotheses. The result is a two-parameter equation given byin which h is the thickness of the layer removed during etching and n is a parameter related to the latent track geometry and etching reaction rate. The equation was compared with experimental data on Australite glass found in the literature and with fresh data on Macusanite glass presented in this work. The model fits the experimental curves quite well, showing that it describes the etching effects correctly (within its limitations). In addition, the model equation derived in this work can be very useful in age correction of partially annealed glass samples. [Copyright &y& Elsevier]

Abstract: The profiles of the proton beams from the Nuclotron accelerator of the Joint Institute for Nuclear Research (JINR) were determined using proton-induced fission in natural lead. Mica track detectors were used to register the fission tracks from NatPb(p, f) reactions. Results for proton beams at energies of 0.75, 1, 1.5 and 2GeV are presented. The MCNPX 2.5e code was used to simulate the interaction of the protons of different energies with a cylindrical lead target of diameter 8.4cm and length 48cm. The effects of the beam profile and the position of the beam centroid on the target, on the spatial distribution of the secondary spallation particles around the target, were investigated. [Copyright &y& Elsevier]

Abstract: In accelerator driven systems, particularly near the spallation target, the neutron spectrum covers a very wide range of energies and has a complex angular distribution. It is possible to determine the fission rate of fissionable nuclei in such neutron fields using fission track technique. We use the mean density of fission tracks in the two track detectors in contact with two faces of a fission foil (radiator). A calibration factor, , relating the number of fission events to the track density is needed and was determined in a very well-known neutron field. It was used to estimate the fission rate in a uranium–lead assembly when the lead target was irradiated with protons of energy 1GeV. Experimental results are compared with Monte Carlo predictions using MCNPX code. [Copyright &y& Elsevier]