Project of a superfluid He3 detector for direct detection of non-baryonic dark matter : MACHe3

MACHe3 (MAtrix of Cells of superfluid Helium 3) is a project of non-baryonic Dark Matter search using superfluid He3 as sensitive medium. Simulations on a high granularity matrix show very good rejection against background events. First results on a prototype cell are very encouraging. Neutron detection has been highlighted as well as cosmic muon detection. A phenomenological study has been done with the DarkSUSY code to investigate complementarity of MACHe3 with existing Dark Matter detectors.Comment: 5 pages, 5 figures, to appear in Proceedings of the 4th Marseille International Cosmology Conferenc

MACHe3, a prototype for non-baryonic dark matter search: KeV event detection and multicell correlation

Superfluid He3 at ultra-low temperatures (100 microKelvins) is a sensitive medium for the bolometric detection of particles. MACHe3 (MAtrix of Cells of Helium 3) is a project for non-baryonic dark matter search using He3 as a sensitive medium. Simulations made on a high granularity detector show a very good rejection to background signals. A multicell prototype including 3 bolometers has been developed to allow correlations between the cells for background event discrimination. One of the cells contains a low activity Co57 source providing conversion electrons of 7.3 and 13.6 keV to confirm the detection of low energy events. First results on the multicell prototype are presented. A detection threshold of 1 keV has been achieved. The detection of low energy conversion electrons coming from the Co57 source is highlighted as well as the cosmic muon spectrum measurement. The possibility to reject background events by using the correlation among the cells is demonstrated from the simultaneous detection of muons in different cells

Ferromagnetism of 3^3He Films in the Low Field Limit

We provide evidence for a finite temperature ferromagnetic transition in 2-dimensions as $H \to 0$ in thin films of $^3$He on graphite, a model system for the study of two-dimensional magnetism. We perform pulsed and CW NMR experiments at fields of 0.03 - 0.48 mT on $^3$He at areal densities of 20.5 - 24.2 atoms/nm$^2$. At these densities, the second layer of $^3$He has a strongly ferromagnetic tendency. With decreasing temperature, we find a rapid onset of magnetization that becomes independent of the applied field at temperatures in the vicinity of 1 mK. Both the dipolar field and the NMR linewidth grow rapidly as well, which is consistent with a large (order unity) polarization of the $^3$He spins.Comment: 4 figure

Superfluid 4He dynamics beyond quasiparticle excitations

The dynamics of superfluid 4He at and above the Landau quasiparticle regime is investigated by high precision inelastic neutron scattering measurements of the dynamic structure factor. A highly structured response is observed above the familiar phonon-maxon-roton spectrum, characterized by sharp thresholds for phonon-phonon, maxon-roton and roton-roton coupling processes. The experimental dynamic structure factor is compared to the calculation of the same physical quantity by a Dynamic Many-body theory including three-phonon processes self-consistently. The theory is found to provide a quantitative description of the dynamics of the correlated bosons for energies up to about three times that of the Landau quasiparticles.Comment: 5 pages, 3 figure

Low energy conversion electron detection in superfluid He3 at ultra-low temperature

We report on the first results of the MACHe3 (MAtrix of Cells of Helium 3) prototype experiment concerning the measurement of low energy conversion electrons at ultra-low temperature. For the first time, the feasibility of the detection of low energy electrons is demonstrated in superfluid He3-B cooled down to 100 microK. Low energy electrons at 7.3 keV coming from the K shell conversion of the 14.4 keV nuclear transition of a low activity Co57 source are detected, opening the possibility to use a He3-based detector for the detection of Weakly Interacting Massive Particles (WIMPs) which are expected to release an amount of energy higher-bounded by 5.6 keV.Comment: 8 pages, 3 figures, to appear in NIM

Landau-Zener Transition in a Continuously Measured Single-Molecule Spin Transistor

We monitor the Landau-Zener dynamics of a single-ion magnet inserted into a spin-transistor geometry. For increasing field-sweep rates, the spin reversal probability shows increasing deviations from that of a closed system. In the low-conductance limit, such deviations are shown to result from a dephasing process. In particular, the observed behaviors are successfully simulated by means of an adiabatic master equation, with time averaged dephasing (Lindblad) operators. The time average is tentatively interpreted in terms of the finite time resolution of the continuous measurement

Paneles solares del SAC-D/aquarius: análisis de los datos de telemetría del primer año en órbita

El satélite SAC-D/Aquarius fue puesto en órbita el 10 de junio de 2011 con paneles solares desarrollados e integrados en la Comisión Nacional de Energía Atómica (CNEA). Utilizando códigos numéricos desarrollados en la CNEA, se realizó una simulación de la característica tensión – corriente y la estimación de la potencia generada en condiciones normalizadas para cada módulo. Se utilizó también un modelo térmico unidimensional para estimar la temperatura del panel solar considerando condiciones estacionarias de transferencia térmica entre ambas caras del panel. En este trabajo se presentan parte de los análisis de datos telemétricos (eléctricos y de temperatura) recibidos desde el lanzamiento hasta fines de junio de 2012 y su comparación con las simulaciones teóricas. Se observa un buen acuerdo entre los datos recibidos por telemetría y las simulaciones, pudiéndose concluir que los paneles solares funcionan adecuadamente y que no se han detectado, durante el período analizado, diferencias en sus características eléctricas asociadas a daño por radiación.Aquarius/SAC-D space mission was launched on June 10, 2011. The Solar Array for this mission has been developed and integrated in the Argentine National Atomic Energy Commission (CNEA). The evaluation of the electrical characteristics and the expected power generation of each module of the Solar Array has been performed by means of a numerical code developed at CNEA. Moreover, a one dimensional thermal model was used for estimating the solar panels temperatures, considering steady state conditions for the thermal transfer between the front and rear faces. In this paper, the analysis of some of the telemetry data received between launch and June 2012 and the comparison with theoretical simulations are presented. The good agreement between measured values and simulations allows to conclude that the Solar Array is working according to expectations and that no experimental evidence of electrical degradation due to radiation damage has been observed during this period.Asociación Argentina de Energías Renovables y Medio Ambiente (ASADES

Electron - nuclear recoil discrimination by pulse shape analysis

In the framework of the ``ULTIMA'' project, we use ultra cold superfluid 3He bolometers for the direct detection of single particle events, aimed for a future use as a dark matter detector. One parameter of the pulse shape observed after such an event is the thermalization time constant. Until now it was believed that this parameter only depends on geometrical factors and superfluid 3He properties, and that it is independent of the nature of the incident particles. In this report we show new results which demonstrate that a difference for muon- and neutron events, as well as events simulated by heater pulses exist. The possibility to use this difference for event discrimination in a future dark matter detector will be discussed.Comment: Proseedings of QFS 2007, Kazan, Russia; 8 pages, 4 figures. Submited to J. Low Temp. Phy

Sistema fotovoltaico conectado a red en el Palacio de Hacienda: análisis de la generación en un año y estudio de sombras

En el marco del proyecto IRESUD, en marzo de 2015 se instaló un sistema fotovoltaico conectado a la red eléctrica en la terraza del Palacio de Hacienda, sito en la calle Hipólito Yrigoyen 250 de la Ciudad Autónoma de Buenos Aires. En el presente trabajo se muestran las comparaciones entre las mediciones de la energía inyectada a la red durante el período abril 2015 - marzo 2016 y las obtenidas con simulaciones mediante el programa comercial PVSyst, así como el estudio de las pérdidas causadas por las sombras sobre el sistema.In the frame of Iresud Project, in March 2015 a grid connected photovoltaic system was installed on the terrace of the “Palacio de Hacienda”, headquarters of the Ministry of Economy, in Buenos Aires city. In this paper, comparisons between measurements of the energy injected to the grid during the period April 2015 - March 2016 and those obtained with simulations using the commercial program PVSyst are shown. Losses caused by near shadows on the system are also analyzed.Tema 13: Generación distribuida.Facultad de Arquitectura y Urbanism

Single-molecule devices with graphene electrodes

Several technological issues have to be faced to realize devices working at the single molecule level. One of the main challenges consists of defining methods to fabricate electrodes to make contact with single molecules. Here, we report the realization of novel spintronic devices made of a TbPc2 single molecule embedded between two nanometer-separated graphene electrodes, obtained by feedback-controlled electroburning. We demonstrate that this approach allows the realisation of devices working at low temperature. With these, we were able to characterize the magnetic exchange coupling between the electronic spin of the Tb3+ magnetic core and the current passing through the molecular system in the Coulomb blockade regime, thus showing that the use of graphene is a promising way forward in addressing single molecules