ESR dating of optically bleached quartz grains: assessing the impact of different experimental setups on dose evaluations

The samples used in the present study have been collected from Bizat Ruhama site with the support of Y. Zaidner, from the University of Haifa, Israel. V.G. research stay in the Australian Research Centre for Human Evolution at Griffith University was funded by a Jose Castillejo Mobility Fellowship CAS18/00285 from the Spanish Ministry of Science, Innovation and Universities. Aspects of this study have been funded by the Australian Research Council Future Fellowship grant FT150100215 granted to M.D.In recent years, our investigation has been centred on improving the reliability and accuracy of the ESR method applied to quartz grains. As part of this ongoing investigation, we present an intra-laboratory study to evaluate the impact of different experimental setups on the ESR measurement precision and dose evaluation for ESR dating of optically bleached quartz grains. Repeated measurements of quartz samples have been performed at CENIEH, Spain, using two different Bruker spectrometers (EMXmicro and Elexsys E500) and resonators (standard rectangular ER4102ST and cylindrical Super High QE cavities). Their performance in terms of sensitivity, measurement repeatability and dose determination are presented in this study. This intra-laboratory work has allowed to evaluate the robustness of our protocol for ESR dating of quartz grains and to study the potential impact of different experimental setups on dose evaluation, which is essential for future standardization of the ESR dating method. Our results indicate that all the different experimental setups provide comparable precision of the ESR intensity measurements. Moreover, all the ESR dose estimates are within 1-sigma error, suggesting that it is possible to compare results obtained by different laboratories when similar analytical procedures are followed. Finally, the higher sensitivity achieved by the SHQE resonator appears to be of particular interest when dealing with samples showing low ESR signal intensities.Spanish Government CAS18/00285Australian Research Council FT15010021

To what extent do field conditions affect gamma dose rate determination using portable gamma spectrometry?

Field gamma spectrometry is a widely used approach for determining in situ gamma dose rates in dosimetric (i.e., electron spin resonance and luminescence) dating applications. In comparison with laboratory-based determinations, in situ radioactivity measurements typically provide more representative gamma dose rate evaluations for heterogeneous sedimentary environments. However, it is often not possible to perform in situ gamma spectrometry measurements under carefully controlled conditions that are directly comparable to those originally used for equipment calibration. In this study, we use Geant4 Monte Carlo simulations to model gamma spectrometry measurements under a range of field conditions, and examine the relative impacts of the following parameters on dose rate determination using the threshold calibration approach: (i) geometry and depth of the measurement hole in which the probe is inserted, (ii) nature of the sediment or rock materials and their water content, (iii) geometry of the radiation environment surrounding the measurement hole, i.e. closed and partially closed sites (e.g., caves, trenches) versus open-air sites (e.g. plain field excavations, cliff or cutting exposures). Our results show that some differences in calibration and field measurement configurations can significantly bias in situ gamma dose rate determinations. Variations in the depth of probe holes can result in underestimations of infinite matrix gamma dose rates by 5% for a 30 cm-deep hole to 58% for measurements made against sediment surfaces (i.e., 2π geometry). Use of hole shapes that do not match those of the probe can lead to underestimations of infinite matrix dose rates by up to 4%, with these biasing effects becoming more significant for shallow holes. External gamma radiation originating from, and backscattered against, structures in the surrounding environment can contribute significantly to gamma dose rates measured using shallow probe holes. The nature of the mineral materials can have a small effect on the measured gamma dose rate (equivalent to infinite matrix dose rate biases of a few percent), mostly due to differences in the density of different materials. Measurements performed in materials with high water contents can be affected by small gamma dose rate overestimations due to differences in water attenuation factors of centimetre-scale objects such as gamma spectrometer probes and those of relevance for dating smaller objects such as sediment grains. These problems can be resolved by using specific correction factors, by including additional uncertainties during dose rate determination, or by performing in situ measurements at different depths for the same location

ESR dating of fluvial deposits from the Middle Tagus Basin (Central Spain): new numerical age results for the Acheulean sites of Pinedo and Cien Fanegas (Abstract)

Depto. de Prehistoria, Historia Antigua y ArqueologíaFac. de Geografía e HistoriaTRUEpu

Deprotometalation-iodolysis and computed CH acidity of 1,2,3- and 1,2,4-triazoles. Application to the synthesis of resveratrol analogues

International audience1-Aryl- and 2-aryl-1,2,3-triazoles were synthesized by N-arylation of the corresponding azoles using aryl iodides. The deprotometalations of 1-phenyl-1,2,3-triazole and -1,2,4-triazole were performed using a 2,2,6,6-tetramethylpiperidino-based mixed lithium-zinc combination and occurred at the most acidic site, affording by iodolysis the 5-substituted derivatives. Dideprotonation was noted from 1-(2-thienyl)-1,2,4-triazole by increasing the amount of base. From 2-phenyl-1,2,3-triazoles, and in particular from 2-(4-trifluoromethoxy)phenyl-1,2,3-triazole, reactions at the 4 position of the triazolyl, but also ortho to the triazolyl on the phenyl group, were observed. The results were analyzed with the help of the CH acidities of the substrates, determined in THF solution using the DFT B3LYP method. 4-Iodo-2-phenyl-1,2,3-triazole and 4-iodo-2-(2-iodophenyl)-1,2,3-triazole were next involved in Suzuki coupling reactions to furnish the corresponding 4-arylated and 4,2’-diarylated derivatives. When evaluated for biological activities, the latter (which are resveratrol analogues) showed moderate antibacterial activity and promising antiproliferative effect against MDA-MB-231 cell line

Direct ESR dating of the Pleistocene vertebrate assemblage from Khok Sung locality, Nakhon Ratchasima Province, Northeast Thailand

We report here the first direct dating study of the faunal assemblage from Khok Sung locality, Thailand. This palaeontological site is of great biochronological, palaeoenvironmental and biogeographical significance. Firstly, it has yielded a rich and diversified Pleistocene vertebrate fauna with up to 15 mammalian species from 13 genera, 10 reptile species, as well as fish and bird remains. Interestingly, while most of the mainland Southeast Asian Pleistocene mammal fossils originate from cave deposits, the Khok Sung fossil layer is located within an 8 m thick fluvial terrace. Secondly, it is geographically located in an area of major importance for reconstructing the migration pathway of large mammals between South China and Java. Combined US-ESR dating of five teeth provides two possible ages of 130 - 29 ka and 217 - 36 ka for the fossils. The reason for the occurrence of these two age groups lies in the fact that it was not possible to obtain sediments that were directly associated with the measured samples, nor was it possible to carry out in situ gamma dose rate measurements due to the high water level. Sediment samples recovered from museum specimens show significantly variable concentrations of radioelements. Both options are equally plausible, as independent methods did not provide firm evidence favouring one or the other age range. The results illustrate the intrinsic limitations of the ESR dating method when fossil teeth are not collected in situ during the excavation. Regardless whether the age of the Khok Sung fauna corresponds to MIS 7 or early MIS5, it is nevertheless one of the oldest assemblages directly dated in the region. Further efforts are required for more accurate fossil identification and attribution and for additional numerical dating in this region to improve the biochronological framework of the Pleistocene mammalian faunas in Southeast Asia, which presently remains quite imprecise.Aspects of this study have been funded by the Australian Research Council Future Fellowship grant FT150100215 granted to M.D., an ANU-CSC Scholarship to F.F., and by the C.N.R.S. “Eclipse” Program and the Department of Mineral Resources (Bangkok)