88 research outputs found

    Procesos sedimentarios y diagenéticos en el registro arqueológico del yacimiento pleistoceno de la Cueva de El Esquilleu (Picos de Europa, Norte de España)

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    La cueva de El Esquilleu (Cillórigo de Liébana, Cantabria, N de España) es un gran abrigo rocoso situado en la región de Picos de Europa (Cordillera Cantábrica) que contiene un importante registro sedimentario, arqueológico y paleontológico del Pleistoceno superior, con abundantes evidencias de industrias líticas musterienses y restos óseos de mamíferos y otros vertebrados. La secuencia estratigráfica se compone de 41 niveles agrupados en cuatro unidades litoestratigráficas con diferente significado sedimentario, que han sido estudiadas con metodología geoarqueológica y tafonómica. En la unidad inferior hemos detectado una acumulación de hidroxilapatito de origen diagenético, que hemos estudiado mediante difracción de rayos X (DRX), microscopía electronica de barrido ambiental (MEBA) y termoluminiscencia (TL). Las dataciones radiocarbónicas existentes y su calibración permiten situar este interesante registro durante el OIS 3 en una horquilla temporal comprendida aproximadamente entre 60000 y 37000 BP.El Esquilleu cave (Cillórigo de Liébana, Cantabria, North of Spain) is a rockshelter placed in the Picos de Europa region (Cantabrian Range) that contains an important sedimentary, archaeological and palaeontological record of the Upper Pleistocene (OIS 3) with abundant mousterian lithics industries and bone remains of mammals and others vertebrates. The stratigraphic sequence consists of 41 levels grouped in four litostratigraphic units with different sedimentary meaning studied by geoarchaeological and taphonomical methods. In the low unit we have detected important accumulations of hydroxylapatite of diagenetic origin, studied by X-ray diffraction (XRD), environmetal scanning electron microscopy (ESEM) and thermoluminescence (TL). The radiocarbon dates existing and their calibration allow approximately locate this interesting record during OIS 3 in a temporary bracket between 60000 and 37000 BP

    Behaviour of advanced tritium breeder pebbles under simultaneous action of accelerated electrons and high temperature

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    The authors greatly acknowledge the technical and experimen-tal support of O. Valtenbergs and L. Avotina (Institute of Chemical Physics, University of Latvia). The work is performed in the frames of the University of Latvia financed project No. Y9-B044-ZF-N-300, “Nano, Quantum Technologies, and Innovative Materials for Eco-nomics”.Advanced lithium orthosilicate (Li4SiO4) pebbles with additions of lithium metatitanate (Li2TiO3) as a secondary phase are suggested as a potential source for tritium breeding in future nuclear fusion reactors. The advanced Li4SiO4 pebbles with different contents of Li2TiO3 were examined before and after simultaneous action of 5 MeV accelerated electron beam (dose rate: up to 10 MGy h−1) and high temperature (up to 1120 K) in a dry argon atmosphere. The accumulated radiation-induced defects (RD) and radiolysis products (RP) were studied by electron spin resonance (ESR) spectrometry and thermally stimulated luminescence (TSL) technique. The phase transitions were studied with powder X-ray diffraction (p-XRD). The microstructure and mechanical strength of the pebbles, before and after irradiation, were investigated by scanning electron microscopy (SEM) and comprehensive crush load tests. The obtained results revealed that the irradiation temperature has a significant impact on the accumulation of RD and RP in the advanced Li4SiO4 pebbles, and with an increasing content of Li2TiO3, the concentration of accumulated paramagnetic RD and RP decreases. Major changes in the mechanical strength, microstructure and phase composition of the advanced pebbles were not detected after irradiation.University of Latvia Y9-B044-ZF-N-300; Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART

    Reinvestigación de los ocres de antimonio históricos de cervantitas-tipo

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    Antimony ocher are yellowish antimony oxo-hydroxides formed by weathering of stibnite (Sb2S3). They occur naturally as single crystallized phases in the isometric system with pyrochlore type structure, containing some Ca and water molecules in the structure, its range in composition can be expressed by the formula: Sb5+ 2-x (Sb3+, Ca)y (O, OH, H2O)6-7, in which y is generally near 1, and x ranges from 0 to 1. Furthermore, Sb-ochres use to include substitutional As, Fe, Ta, Ti, Cu and others. This chemical variability keeping the structure has generated historical confusion of names of equivalent minerals with similar X-ray diffraction patterns being necessary the use of additional techniques. The mineral-type Cervantite from Cervantes (Spain) (Ca, Sb3+)2(Sb5+)2O6(OH) was disapproved at 1954 and re-approved at 1962 as α-Cervantite Sb3+Sb5+O4 analyzing synthetic and natural antimony ochres from other localities, e.g., Brasina (Serbia) by X-ray diffraction. We herein characterize both historical specimens-type from Cervantes (Lugo, Spain) and Zajaca-Stolice (Brasina, Serbia) from the chemical-elemental, structural, thermal and speciation points of view, together with a vibrational study by Raman and FTIR, since the X-ray diffraction patterns of isometric samples with pyrochlore-type structure are excessively similar among them. The Cervantes specimen-type could be named hydroxycalcioromeite (Ca, Sb3+)2(Sb5+)2O6(OH) whereas the Brasina specimen-type Ca2(Sb5+)4O12(OH)2 is very similar but lacking Sb3+; both specimens contain Ca and hydrous components, faraway of the official anhydrous orthorhombic α-Cervantite (Sb3+Sb5+O4) setting. Micro-Raman was essential determining molecular phases and Sb-O bond vibrations, FTIR and DTA-TG finding hydroxyl groups and XPS defining Sb speciation.Los ocres de antimonio son óxi-hidróxidos formados por meteorización de estibnita (Sb2S3). Normalmente aparecen como fases minerales simples cristalizadas en el sistema cúbico con estructura de tipo pirocloro y conteniendo algo de calcio y moléculas de agua en su red cristalina. Sus rangos composicionales pueden ser expresados por la fórmula: Sb5+ 2-x (Sb3+, Ca)y (O, OH, H2O)6-7, donde (y) está cerca de 1 y (x) va de 0 a 1. También es muy frecuente que los ocres de antimonio incluyan sustituciones de As, Fe, Ta, Ti, Cu y otros. Esta variabilidad química dentro de la misma estructura ha generado confusiones históricas de nombres de minerales equivalentes con patrones de difracción de rayos X muy similares siendo importante complementar con técnicas analíticas adicionales. El mineral-tipo cervantita de Cervantes (Lugo, España) (Ca, Sb3+)2(Sb5+)2O6(OH) fue desacreditado en 1954 y re-aprobado en 1962 como α-cervantita Sb3+Sb5+O4 difractando muestras de óxidos de antimonio sintéticos y naturales de otras localidades, como por ejemplo de Brasina (Serbia). En este trabajo estudiamos ambos minerales-tipo de Cervantes (Lugo, Spain) y de Zajaca-Stolice (Brasina, Serbia) desde los puntos de vista estructural, químico-elemental, termal, vibracional y de especiación química, asumiendo que los patrones de difracción de rayos X, los de la estructura tipo pirocloro son muy similares entre ellos. El espécimen tipo de Cervantes (Lugo) puede ser considerado como hydroxycalcioromeita (Ca,Sb3+)2(Sb5+)2O6(OH) mientras que el de Brasina Ca2(Sb5+)4O12(OH)2 es muy similar pero sin Sb3+. Ambas muestras contienen calcio y componentes hidratados, es decir, ambos están lejos de ser la α-Cervantita (Sb3+Sb5+O4) oficial anhidra y ortorrómbica. La espectroscopia micro-Raman es esencial para determinar fases minerales y vibraciones de enlaces Sb-O, mientras que espectroscopia FTIR y los ATD-TG fueron útiles para determinar grupos hidroxilos y aguas moleculares y la espectroscopia XPS para definir las especiaciones químicas del antimonio

    Review of retrospective dosimetry techniques for external ionising radiation exposures

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    The current focus on networking and mutual assistance in the management of radiation accidents or incidents has demonstrated the importance of a joined-up approach in physical and biological dosimetry. To this end, the European Radiation Dosimetry Working Group 10 on 'Retrospective Dosimetry' has been set up by individuals from a wide range of disciplines across Europe. Here, established and emerging dosimetry methods are reviewed, which can be used immediately and retrospectively following external ionising radiation exposure. Endpoints and assays include dicentrics, translocations, premature chromosome condensation, micronuclei, somatic mutations, gene expression, electron paramagnetic resonance, thermoluminescence, optically stimulated luminescence, neutron activation, haematology, protein biomarkers and analytical dose reconstruction. Individual characteristics of these techniques, their limitations and potential for further development are reviewed, and their usefulness in specific exposure scenarios is discussed. Whilst no single technique fulfils the criteria of an ideal dosemeter, an integrated approach using multiple techniques tailored to the exposure scenario can cover most requirements. © The Author 2010. Published by Oxford University Press. All rights reserved

    Aplicación de la termoluminiscencia de aluminosilicatos alcalinos a la dosimetria ambiental retrospectiva

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    Este trabajo ha sido posible gracias a la financiación de: La UE a través del proyecto 'Dose Reconstructiorl (FI4P-CT 95-0011d). El CSN con el proyecto 'Dosimetría Retrospectiva (DOSEl (acuerdo• CIEMAT-CSN 96/208). Y La DGICYT con el proyecto 'Implicaciones de la luminiscencia espectral de feldespatos alcalinos en alteración de granito, dosimetría ambiental y datación geológica' (PB 95-0108)Peer Reviewe

    Effects of different UV exposures on the thermoluminescence of high albite

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    High albite can be used as a new UV dosimeter. Heated natural albite posseses a special property: it has strong thermoluminescence (TL) blue emissions under UV radiation. The TL glow curves of high albite after different times of UV exposure show PhotoTransferred ThermoLuminescence (PTTL) from deeps traps (345oC - 450oC) to shallow traps (150oC) which can be used to store UV damage. The point of inflexion of the process occurs after one hour under UV radiation, the low temperature peaks start gaining in intensity while the high temperature peaks stop dropping and stabilize into a plateau. Samples which have been subjected to UV radiation for 1 hour at different temperatures (RT, 70oC, 105oC and 140oC) give glow curves which display an increase of the maxima peaks according to temperature (up to 300oC). High albite, UV irradiated (for one hour) at 70oC displays a TL signal decrease of 30% after 1000 hours of storage at room temperature with high intensity emissions, for this reason this material could be a good UV dosimeter.Peer Reviewe

    A new classification of feldspars by luminescence spectral techniques

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    The proposed luminescence classification of feldspars is found on the relationships between feldspar lattice defects and their coupled spectra luminescence peaks. The UV emission at 290 nm is linked with the presence of Na and cracks-strain-exsolution-twinning; at 340 nm with stress in Si¿O bonds; the broad blue band (380-450nm) with [AlO4]o defects; at 560nm with Mn2+ point defects and at 720nm with iron in the lattice. The feldspar classification here provided can be used as a practical guideline for pegmatite feldspar studies since the luminescence techniques are sensitive tools detecting defects.Peer Reviewe

    Thermo- and cathodoluminescence properties of lepidolite

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    Lepidolite, K(Li,Al)3(Si,Al)4O10(F,OH)2, and many of the related phyllosilicate mineral of the mica group have been well studied from the chemical and structural point of view; however, to the best of our knowledge, studies on their luminescence properties have been scarcely reported. This work focuses on the thermoluminescence (TL) and cathodoluminescence (CL) response of a natural lepidolite from Portugal previously characterized by means of environmental scanning electron microscope (ESEM) and X-ray fluorescence (XRF) and atomic absorption spectroscopy (AAS) techniques. The complexity of the thermoluminescence glow curves of non-irradiated and 1Gy irradiated samples suggests a structure of a continuous trap distribution involving multiorder kinetics. UV-IR CL spectral emission shows seven peaks centered at 330, 397, 441, 489, 563, 700 and 769 nm. Such emission bands could be due to (i) structural defects, i. e. [AlO4] or non-bridging oxygen hole centers, and (ii) the presence of point defects associated with Mn2+ and Fe3+.Peer Reviewe

    Characterization of natural and induced UV-blue thermoluminescence properties of kaolinite

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    The UV-blue thermoluminescence (TL) emission of natural kaolinite has been investigated to determine its potential use in the field of dating and retrospective dosimetry. This paper focuses on: (i) The dose dependence of the 400nm TL intensity of kaolinite that exhibits an excellent linearity in the range of 50mGy-8Gy. (ii) The stability of the induced TL signal after six months of storage, shows an initial rapid decay (ca. 45%) maintaining the stability from 40 days onwards which indicates that the electron population decreases asymptotically by the X-axis and the involved electrons are located in deeper traps at room temperature. The fading process can be fitted to a first order decay equation of the sort y=y0+A exp (-x/t). (iii) The tests of thermal stability at different temperatures allow us to speculate in a continuous trap distribution with progressive changes in the glow curve shape, intensity and temperature position of the maximum peak. According to this behaviour some physical parameters have been estimated.Peer Reviewe
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