Light yield determination in large sodium iodide detectors applied in the search for dark matter

Application of NaI(Tl) detectors in the search for galactic dark matter particles through their elastic scattering off the target nuclei is well motivated because of the long standing DAMA/LIBRA highly significant positive result on annual modulation, still requiring confirmation. For such a goal, it is mandatory to reach very low threshold in energy (at or below the keV level), very low radioactive background (at a few counts/keV/kg/day), and high detection mass (at or above the 100 kg scale). One of the most relevant technical issues is the optimization of the crystal intrinsic scintillation light yield and the efficiency of the light collecting system for large mass crystals. In the frame of the ANAIS (Annual modulation with NaI Scintillators) dark matter search project large NaI(Tl) crystals from different providers coupled to two photomultiplier tubes (PMTs) have been tested at the Canfranc Underground Laboratory. In this paper we present the estimates of the NaI(Tl) scintillation light collected using full-absorption peaks at very low energy from external and internal sources emitting gammas/electrons, and single-photoelectron events populations selected by using very low energy pulses tails. Outstanding scintillation light collection at the level of 15~photoelectrons/keV can be reported for the final design and provider chosen for ANAIS detectors. Taking into account the Quantum Efficiency of the PMT units used, the intrinsic scintillation light yield in these NaI(Tl) crystals is above 40~photoelectrons/keV for energy depositions in the range from 3 up to 25~keV. This very high light output of ANAIS crystals allows triggering below 1~keV, which is very important in order to increase the sensitivity in the direct detection of dark matter

Background analysis and status of the ANAIS dark matter project

ANAIS (Annual modulation with NaI Scintillators) is a project aiming to set up at the new facilities of the Canfranc Underground Laboratory (LSC), a large scale NaI(Tl) experiment in order to explore the DAMA/LIBRA annual modulation positive result using the same target and technique. Two 12.5 kg each NaI(Tl) crystals provided by Alpha Spectra took data at the LSC in the ANAIS-25 set-up. The comparison of the background model for the ANAIS-25 prototypes with the experimental results is presented. ANAIS crystal radiopurity goals have been achieved for Th-232 and U-238 chains, but a Pb-210 contamination out-of-equilibrium was identified, whose origin has been studied. The high light collection efficiency obtained with these prototypes allows to anticipate an energy threshold of the order of 1 keVee. A new detector, with improved performances, was received in March 2015 and very preliminary results are shown.Comment: 6 pages, 7 figure

Análisis del relieve y cartografía de procesos geomorfológicos activos mediante SIG en la zona de confluencia de los ríos Tuerto y Porquera (provincia de León, España)

La configuración del relieve terrestre y los cambios que tienen lugar en el entorno natural de los asentamientos humanos tienen una gran trascendencia social y económica debido a que marcan las condiciones de habitabilidad y desarrollo futuro de las actividades antrópicas. Partiendo de este hecho, el principal objetivo de este estudio es la realización de una cartografía geomorfológica en la cual aparezcan reflejados los principales procesos activos de tipo geológico, como base para la realización en el futuro de estudios de susceptibilidad de riesgos geológicos y determinar las zonas en las que la ocupación humana pueda verse afectada por daños relacionados con procesos naturales relacionados con el medio físico. Para la elaboración de esta cartografía geomorfológica se han realizado tareas de fotointerpretación en visión estereoscópica y representación en un Sistema de Información Geográfica (ArcGis 10.1), utilizando como base el Modelo Digital del Terreno MDT05/MDT05-LIDAR con una resolución espacial de 5x5 metros, aplicando distintas herramientas, utilizando también la capa de la BCN25 de curvas de nivel, así como trabajo de campo de comprobación y descripción del relieve y procesos activos. En el mapa obtenido se pueden distinguir tres tipos de dominios geomorfológicos, cada uno con sus procesos geológicos activos predominantes: dominio paleozoico con procesos gravitacionales, dominio neógeno con procesos gravitacionales y de erosión y, por último, dominio fluvial con presencia de abanicos aluviales y llanuras de inundación principalmente

Preliminary results of ANAIS-25

The ANAIS (Annual Modulation with NaI(Tl) Scintillators) experiment aims at the confirmation of the DAMA/LIBRA signal using the same target and technique at the Canfranc Underground Laboratory. 250 kg of ultrapure NaI(Tl) crystals will be used as a target, divided into 20 modules, each coupled to two photomultipliers. Two NaI(Tl) crystals of 12.5 kg each, grown by Alpha Spectra from a powder having a potassium level under the limit of our analytical techniques, form the ANAIS-25 set-up. The background contributions are being carefully studied and preliminary results are presented: their natural potassium content in the bulk has been quantified, as well as the uranium and thorium radioactive chains presence in the bulk through the discrimination of the corresponding alpha events by PSA, and due to the fast commissioning, the contribution from cosmogenic activated isotopes is clearly identified and their decay observed along the first months of data taking. Following the procedures established with ANAIS-0 and previous prototypes, bulk NaI(Tl) scintillation events selection and light collection efficiency have been also studied in ANAIS-25.Comment: 4 pages, 6 Figure

Bulk NaI(Tl) scintillation low energy events selection with the ANAIS-0 module

Dark matter particles scattering off some target nuclei are expected to deposit very small energies in form of nuclear recoils (below 100 keV). Because of the low scintillation efficiency for nuclear recoils vs. electron recoils, in most of the scintillating targets considered in the search for dark matter, the region below 10 keVee concentrates most of the expected dark matter signal. For this reason, very low energy threshold (at or below 2 keVee) and very low background are required. This is the case of the ANAIS (Annual modulation with NaI Scintillators) experiment. A good knowledge of the detector response function for real scintillation events, a good characterization of other anomalous or noise event populations contributing in that energy range, and the development of convenient filtering procedures for the latter are mandatory to achieve the required low background at such a low energy. In this work we will present the specific protocols developed to select bulk scintillation events in NaI(Tl), and its application to data obtained with the ANAIS-0 prototype. Slight differences in time constants are expected in scintillation pulses produced by nuclear or electron recoils in NaI(Tl), so in order to analyze the effect of these filtering procedures in the case of a recoil population attributable to dark matter, data from a neutron calibration have been used.Comment: 13 pages, 22 figure

Role of the Renin-Angiotensin System and Aldosterone on Cardiometabolic Syndrome

Aldosterone facilitates cardiovascular damage by increasing blood pressure and through different mechanisms that are independent of its effects on blood pressure. In this respect, recent evidence involves aldosterone in the pathogenesis of metabolic syndrome. Although this relationship is complex, there is some evidence suggesting that different factors may play an important role, such as insulin resistance, renin-angiotensin-aldosterone system, oxidative stress, sodium retention, increased sympathetic activity, levels of free fatty acids, or inflammatory cytokines and adipokines. In addition to the classical pathway by which aldosterone acts through the mineralocorticoid receptors leading to sodium retention, aldosterone also has other mechanisms that influence cardiovascular tissue remodelling. Finally, overweight and obesity promote the adrenal secretion of aldosterone, increasing the predisposition to type 2 diabetes mellitus. Further studies are needed to better establish therapeutic strategies that act on the blockade of mineralocorticoid receptor in the treatment and prevention of cardiovascular diseases related to the excess of aldosterone and the metabolic syndrome

Influence of the substrate type on CVD grown homoepitaxial diamond layer quality by cross sectional TEM and CL analysis

To assess diamond-based semiconducting devices, a reduction of point defect levels and an accurate control of doping are required as well as the control of layer thickness. Among the analyses required to improve such parameters, cross sectional studies should take importance in the near future. The present contribution shows how FIB (focused ion beam) preparations followed by electron microscopy related techniques as TEM or CL allowed to performanalysis versus depth in the layer, doping and point defect levels. Three samples grown along the sameweek in the same machinewith identical growth conditions but on different substrates (CVD-IIIa (110) oriented, CVD-optical grade (100) oriented and a HPHT-Ib (100) oriented) are studied. Even though A-band is observed by CL, no dislocation is observed by CTEM. Point defect type and level are shown to substantially change with respect to the substrate type as well as the boron doping levels that vary within an order of magnitude. H3 present in the epilayer grown on HPHT type of substrate is replaced by T1 and NE3 point defects for epilayers grown on the CVD type one. An increase of excitonic transitions through LO phonons is also shown to take place near the surface while only TO ones are detected deeper in the epilayer. Such results highlight the importance of choosing the correct substrate.5 page