18 research outputs found
Effect of annealing on the superconducting properties of a-Nb(x)Si(1-x) thin films
a-Nb(x)Si(1-x) thin films with thicknesses down to 25 {\AA} have been
structurally characterized by TEM (Transmission Electron Microscopy)
measurements. As-deposited or annealed films are shown to be continuous and
homogeneous in composition and thickness, up to an annealing temperature of
500{\deg}C. We have carried out low temperature transport measurements on these
films close to the superconductor-to-insulator transition (SIT), and shown a
qualitative difference between the effect of annealing or composition, and a
reduction of the film thickness on the superconducting properties of a-NbSi.
These results question the pertinence of the sheet resistance R_square as the
relevant parameter to describe the SIT.Comment: 9 pages, 12 figure
Identification of backgrounds in the EDELWEISS-I dark matter search experiment
This paper presents our interpretation and understanding of the different
backgrounds in the EDELWEISS-I data sets. We analyze in detail the several
populations observed, which include gammas, alphas, neutrons, thermal sensor
events and surface events, and try to combine all data sets to provide a
coherent picture of the nature and localisation of the background sources. In
light of this interpretation, we draw conclusions regarding the background
suppression scheme for the EDELWEISS-II phase
Axion searches with the EDELWEISS-II experiment
We present new constraints on the couplings of axions and more generic
axion-like particles using data from the EDELWEISS-II experiment. The EDELWEISS
experiment, located at the Underground Laboratory of Modane, primarily aims at
the direct detection of WIMPs using germanium bolometers. It is also sensitive
to the low-energy electron recoils that would be induced by solar or dark
matter axions. Using a total exposure of up to 448 kg.d, we searched for
axion-induced electron recoils down to 2.5 keV within four scenarios involving
different hypotheses on the origin and couplings of axions. We set a 95% CL
limit on the coupling to photons GeV in
a mass range not fully covered by axion helioscopes. We also constrain the
coupling to electrons, , similar to the more
indirect solar neutrino bound. Finally we place a limit on , where is the
effective axion-nucleon coupling for Fe. Combining these results we
fully exclude the mass range keV for DFSZ axions and
keV for KSVZ axions
Final results of the EDELWEISS-I dark matter search with cryogenic heat-and-ionization Ge detectors
The final results of the EDELWEISS-I dark matter search using cryogenic
heat-and-ionization Ge detectors are presented. The final data sample
corresponds to an increase by a factor five in exposure relative to the
previously published results. A recoil energy threshold of 13 keV or better was
achieved with three 320g detectors working simultaneously over four months of
stable operation. Limits on the spin-independent cross-section for the
scattering of a WIMP on a nucleon are derived from an accumulated fiducial
exposure of 62 kg.d.Comment: 42 pages, 16 figures, submitted to Physical Review D, 1 figure and 2
references added, some little changes in the tex
Thick silicon microstrip detectors simulation for PACT: Pair and Compton Telescope
International audiencePACT is a space borne Pair and Compton Telescope that aims to make a sensitive survey of the gamma-ray sky between 100 keV and 100 MeV. It is based upon two main components: a silicon-based gamma-ray tracker and a crystal-based calorimeter. In this paper we will explain the imaging technique of PACT as a Multi-layered Compton telescope (0.1–10 MeV) and its major improvements over its predecessor COMPTEL. Then we will present a simulation study to optimize the silicon tracker of PACT. This tracker is formed of thousands of identical silicon double sided strip detectors (DSSDs). We have developed a simulation model (using SILVACO) to simulate the DSSD performance while varying its thickness, impurity concentration of the bulk material, electrode pitch, and electrode width. We will present a comprehensive overview of the impact of each varied parameter on the DSSD performance, in view of the application to PACT. The considered DSSD parameters are its depletion voltage, capacitance, and leakage current. After the selection of the PACT DSSD, we will present a simulation of the performance of the PACT telescope in the 0.1–10 MeV range
Development of Ge/NbSi detectors for EDELWEISS-II with identification of near-surface events
The actual limitation of Ge ionization heat cryogenic detectors for direct WIMP detection such as EDELWEISS arises from incomplete charge collection for near-surface events. We present results on Ge/NbSi detectors that are fitted with segmented electrodes and two NbSi Anderson insulator thermometric layers. Three such bolometers were studied in the low-background cryostat of the EDELWEISS collaboration in the LSM: analysis of the athermal signals allows us to identify and reject events occurring in the first millimeter under the electrodes
Modelling of the surface-event identification mechanism in Ge detectors equipped with NbSi thin films
A new generation of germanium composite bolometers, equipped with NbSi thin films, has been developed in the framework of the EDELWEISS experiment, presenting impressive surface event identification capabilities and a substantial improvement in the background rejection of heat and ionization detectors. In this work we present a simple thermal model which explain the surface-event identification mechanism via NbSi thin films sensors
Optimization of cryogenic Ge detector equipped with NbSi thin film thermometers: Fiducial volume and energy resolution
Ionisation-heat detectors are very useful in direct detection dark matter experiments because they lead to an active rejection of the background. Their rejection performances are presently limited by near electrode surface events leading to incomplete charge collection. We propose an identification of near NbSi electrodes events based on pulse shape analysis of the phonon signal delivered by the thermometric layer. We discuss recent progress in the near surface event identification accuracy together with the remaining fiducial volume and the heat channel resolution
PACT: a sensitive 100 keV-10 MeV all sky Pairs and Compton Telescope
International audiencePACT is a Pair And Compton Telescope that aims to make a sensitive survey of the gamma-ray sky between 100 keV and 100 MeV. It will be devoted to the detection of radioactivity lines from present and past supernova explosions, the observation of thousands of new blazars, and the study of polarized radiations from gamma-ray bursts, pulsars and accreting black holes. It will reach a sensitivity of one to two orders of magnitude lower than COMPTEL/CGRO (e.g. about 50 times lower for the broad-band, survey sensitivity at 1 MeV after 5 years). The concept of PACT will be proposed for the AstroMeV mission in the framework of the M4 ESA Call. It is based upon three main components: a silicon-based gamma-ray tracker, a crystal-based calorimeter (e.g. CeBr3:Sr), and an anticoincidence detector made of plastic scintillator panels. Prototypes of these detector planes are currently tested in the laboratories