Viscosity of polarized liquid3He studied by NMR and related thermodynamics

A new method to measure the magnetization dependence of the viscosity in polarized liquid³He is presented. The magnetization is obtained by brute force polarization at 50 mK in magnetic fields up to 11 T; it is subsequently destroyed by saturation of the NMR signal. Irreversible heating due to the saturation and relaxation of the magnetization is easily observed using the viscometer. Comparison of the calculated temperature evolution with the behavior of the viscometer shows that the viscosity is slightly magnetization dependent. Our result, a relative increase of the viscosity of 0.3±0.15% for a polarization of 3.9% and a pressure of 30 bar, disagrees with a prediction based on the nearly metamagnetic model and the first measurement based on the rapid melting of polarized solid.     

High Q 2D-length extension mode resonators for potential time–frequency applications

Microsystem Technologies - This paper presents recent advances on two dimensional length-extension mode (2D-LEM) quartz resonators providing high quality (Q) factor on resonances at a few MHz. The...     

Considerations on thermal effects in doped scintillators for dark matter and other rare events searches

The scintillation properties of luminescent crystals are well known at room temperature. It is only recently, for the sake of dark matter and rare events searches that the studies have been extended to very low temperatures in the millikelvin range. Some little-known facts on the behaviour of bolometers¹, and more specifically on scintillating ones, are recalled in a simple manner. A few experiments to better understand them are proposed.     

Nb-Si thin films as thermometers for low temperature bolometers

Thin alloy films with compositions leading to the Anderson metal-to-insulator transition can potentially lead to high detection sensitivities and adjustable input impedances as well as to excellent coupling to the heat absorber. We demonstrate some of these advantages in the case of Nb-Si films, whose bias power is shown to be at least 50 times that of NTD Ge detectors at about 30 mK.     

Cryogenic Ge Detectors for Dark Matter Search: Surface Event Rejection with Ionization Signals

A new design of an ionization-heat germanium detector for dark matter search is presented, based on the use of interleaved electrodes for charge collection. This device allows active rejection of surface events by performing the appropriate cuts in the charge measurement data. Test experiments were performed with a prototype device, fitted with annular collection electrodes and with a neutron transmutation-doped Ge thermometer. Calibration runs with gamma and neutron sources demonstrate the remarkable possibilities offered by this type of detector in terms of surface event discrimination.      

Surface Event Rejection of the EDELWEISS Cryogenic Germanium Detectors Based on NbSi Thin Film Sensors

Near-surface-events are a major limitation to the performance of cryogenic massive germanium heat and ionisation detectors for dark matter search, due to their incomplete charge collection. We present here a powerful method of surface event identification based on the transient heat signal of a Ge bolometer, equipped with two NbSi high impedance thin film sensors. Calibration runs using electrons and low energy gamma particles from a ¹⁰⁹Cd source show highly effective surface event rejection down to the heat threshold energy. Neutron and gamma source calibrations were realised to get information on the fiducial volume of the Ge absorber. First results from low background data taking are discussed.     

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.      

Calibration of the EDELWEISS cryogenic heat-and-ionization germanium detectors for dark matter search

Several aspects of the analysis of the data obtained with the cryogenic heat-and-ionization Ge detectors used by the EDELWEISS dark matter search experiment are presented. Their calibration, the determination of their energy threshold, fiducial volume and nuclear recoil acceptance are detailed.     

Measurements of the nuclear spin-lattice relaxation times in BCC3He for high magnetic fields,high molar volumes,and low temperatures

Experimental studies of the nuclear spin-lattice relaxation times in BCC helium three are reported for high molar volumes and low temperatures close to the minimum in the melting curve. The results show the existence of a new relaxation mechanism at low temperatures with an approximately linear temperature dependence (T ₁ T ^–1). An analysis of the vacancy-induced relaxation shows that both the vacancy formation energy and the vacancy mobility decrease dramatically as a function of density on approaching the maximum possible molar volume (minimum density) of the solid. A possible interpretation of both the new relaxation mechanism and the vacancy properties is outlined.