Exploring the Proximity Effect in Mo/Au Bilayers

We report on the sensitivity of superconducting transition temperature (T c ) to the individual layers' thickness in Mo/Au proximity bilayers to be used in transition-edge sensors (TESs). The achieved good reproducibility and quality of the bilayers allow a clear determination of the superconducting critical temperature T c as a function of the Mo and Au thicknesses. One objective of this work is to analyse the quality of the Mo/Au interface and to assess the possible effects of the double Au layer we use to fabricate these bilayers and TESs based on them. Experimental data are analysed on the basis of Usadel equations using the model developed by Martinis and co-workers, in which the proximity effect in the bilayer is mainly governed by the interface transparency between the superconductor and the normal metal. We find that this model describes quite well the behavior of T c , even for quite thick Au layers, and that the double Au layer does not play any relevant role on the proximity effect

Exploring the Proximity Effect in Mo/Au Bilayers

We report on the sensitivity of superconducting transition temperature (T c ) to the individual layers' thickness in Mo/Au proximity bilayers to be used in transition-edge sensors (TESs). The achieved good reproducibility and quality of the bilayers allow a clear determination of the superconducting critical temperature T c as a function of the Mo and Au thicknesses. One objective of this work is to analyse the quality of the Mo/Au interface and to assess the possible effects of the double Au layer we use to fabricate these bilayers and TESs based on them. Experimental data are analysed on the basis of Usadel equations using the model developed by Martinis and co-workers, in which the proximity effect in the bilayer is mainly governed by the interface transparency between the superconductor and the normal metal. We find that this model describes quite well the behavior of T c , even for quite thick Au layers, and that the double Au layer does not play any relevant role on the proximity effect

Prehistoria de la matemática y mente moderna : pensamiento matemático y recursividad en el Paleolítico franco-cantábrico

En este artículo, en primer lugar, se repasan de forma general distintos tipos de registros simbólicos realizados por los grupos prehistóricos desde los más remotos y probables orígenes de la mente humana moderna. A continuación, se revisan algunas de las más destacadas piezas de la Prehistoria relacionadas con el registro matemático, destacando la importancia (por cantidad y calidad), no suficientemente valorada, de las piezas de este tipo de la región franco-cantábrica. La información anterior, finalmente, nos da pie a destacar la tremenda importancia en este contexto de cuatro plaquitas de hueso hioides de caballo de la Cueva de Altamira, datadas en el Solutrense Superior (c. 18.500 años). Estas plaquitas, al ser un conjunto coherente de elementos interrelacionados, se proponen aquí como la representación de una recursividad, cualidad ésta que se ha considerado como propia y exclusiva del lenguaje humano

Large current-induced broadening of the superconducting transition in Mo/Au transition edge sensors

The R(T, I) shape of the superconducting transition in transition edge sensors (TESs) is of crucial importance to determine their ultimate performance. This paper reports a study of the temperature and current dependences of the transition of Mo/Au TESs, focused on the low resistance region, where these devices preferentially operate. A large broadening of the transition is observed when increasing the applied current. An empirical analytic expression for R(T, I) is found, which describes the transition of devices with different critical temperatures, from R = 0 up to at least 30% R-n (in some cases nearly 80% R-n). Several mechanisms for this behaviour are considered; results show that a current assisted vortex pair unbinding mechanism (Berezinskii-Kosterlitz-Thouless transition) could be the possible origin for this behaviour. Finally, the consequences of the current-induced transition broadening for TES properties and operation are outlined

Status of the ANAIS Dark Matter Project at the Canfranc Underground Laboratory

The ANAIS experiment aims at the confirmation of the DAMA/LIBRA signal. A detailed analysis of two NaI(Tl) crystals of 12.5 kg each grown by Alpha Spectra will be shown: effective threshold at 1 keVee is at reach thanks to outstanding light collection and robust PMT noise filtering protocols and the measured background is well understood down to 3 keVee, having quantified K, U and Th content and cosmogenic activation in the crystals. A new detector was installed in Canfranc in March 2015 together with the two previous modules and preliminary characterization results will be presented. Finally, the status and expected sensitivity of the full experiment with 112 kg will be reviewed.Comment: Contributed to the 11th Patras Workshop on Axions, WIMPs and WISPs, Zaragoza, June 22 to 26, 201

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

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 model of NaI(Tl) detectors for the ANAIS Dark Matter Project

A thorough understanding of the background sources is mandatory in any experiment searching for rare events. The ANAIS (Annual Modulation with NaI(Tl) Scintillators) experiment aims at the confirmation of the DAMA/LIBRA signal at the Canfranc Underground Laboratory (LSC). Two NaI(Tl) crystals of 12.5 kg each produced by Alpha Spectra have been taking data since December 2012. The complete background model of these detectors and more precisely in the region of interest will be described. Preliminary background analysis of a new 12.5 kg crystal received at Canfranc in March 2015 will be presented too. Finally, the power of anticoincidence rejection in the region of interest has been analyzed in a 4x 5 12.5 kg detector matrix.Comment: Contributed to the 11th Patras Workshop on Axions, WIMPs and WISPs, Zaragoza, June 22 to 26, 201

Production and relevance of cosmogenic radionuclides in NaI(Tl) crystals

The cosmogenic production of long-lived radioactive isotopes in materials is an hazard for experiments demanding ultra-low background conditions. Although NaI(Tl) scintillators have been used in this context for a long time, very few activation data were available. We present results from two 12.5 kg NaI(Tl) detectors, developed within the ANAIS project and installed at the Canfranc Underground Laboratory. The prompt data taking starting made possible a reliable quantification of production of some I, Te and Na isotopes with half-lives larger than ten days. Initial activities underground were measured and then production rates at sea level were estimated following the history of detectors; a comparison of these rates with calculations using typical cosmic neutron flux at sea level and a selected description of excitation functions was also carried out. After including the contribution from the identified cosmogenic products in the detector background model, we found that the presence of 3H in the crystal bulk would help to fit much better our background model and experimental data. We have analyzed the cosmogenic production of 3H in NaI, and although precise quantification has not been attempted, we can conclude that it could imply a very relevant contribution to the total background below 15 keV in NaI detectors.Comment: Proceedings of the Low Radioactivity Techniques 2015 workshop, March 2015, Seattle (US