69 research outputs found
EDELWEISS dark matter search: Latest results and future plans
International audienceEDELWEISS is a direct search for WIMP dark matter using cryogenic heat-and-ionization germanium detectors. We report the final results of the second stage of the experiment, EDELWEISS-II, obtained with an array of ten 400 g detectors. A total effective exposure of 384 kg.day has been achieved, obtained following fourteen months of continuous operation at the Laboratoire Souterrain de Modane. Five nuclear recoil candidates are observed above 20 keV, while the estimated background is less than 3 events. We also present the prospects of EDELWEISS-III, which plans to accumulate more than 3000 kg.day of data with fourty new 800 g detectors
A gamma- and X-ray detector for cryogenic, high magnetic field applications
As part of an experiment to measure the spectrum of photons emitted in
beta-decay of the free neutron, we developed and operated a detector consisting
of 12 bismuth germanate (BGO) crystals coupled to avalanche photodiodes (APDs).
The detector was operated near liquid nitrogen temperature in the bore of a
superconducting magnet and registered photons with energies from 5 keV to 1000
keV. To enlarge the detection range, we also directly detected soft X-rays with
energies between 0.2 keV and 20 keV with three large area APDs. The
construction and operation of the detector is presented, as well as information
on operation of APDs at cryogenic temperatures
Energy partition in Sapphire and BGO scintillating bolometers
International audienceScintillating bolometers are particle detectors with a high particle discrimination power with many applications in nuclear and particle physics. This discrimination power is based on the different scintillation yield for different particles, and is strongly dependent on the target used. At the very low temperatures required for the operation of the bolometers, very few data about the scintillation yields are available. In this paper we present estimates of absolute light yields and energy partition among heat, light and trapping channels in Sapphire (AlO) and BGO (BiGeO) scintillating bolometers operated at 20Â mK. The estimate relies on the observed negative correlation between the light and heat signals produced by Îł-ray absorption in scintillating bolometers and on the study of the x-ray stimulated luminescence properties of BGO at temperatures down to 77 K
Neutron Spectrometry with Scintillating Bolometers of LiF and Sapphire
Two scintillating bolometers of LiF (33 g) and Al2O3 (50 g) at 20 mK, inside a lead shielding at the Canfranc Underground Laboratory, were irradiated with neutrons from a source of 252Cf. The analysis of nuclear recoils registered by sapphire and (n, a) captures by 6Li shows the feasibility of these cryogenic devices to measure the spectral flux of a neutron field. Data unfolding was done assuming that the spectral flux is a piecewise constant function defined on six energy groups. It can be solved by using non-negative least squares without additional assumptions on the neutron flux. The model provides consistent results with the spectra of the observed events in bolometers, giving a fast neutron flux of F(E > 0.1 MeV) = 0.20 n s-1cm-2 with a 15% uncertainty after 3 hours of live time. After our analysis, it can be concluded that nuclear recoils in sapphire are more useful than (n, a) captures in LiF for spectrometry of fast neutrons
Final results of the EDELWEISS-II WIMP search using a 4-kg array of cryogenic germanium detectors with interleaved electrodes
The EDELWEISS-II collaboration has completed a direct search for WIMP dark
matter with an array of ten 400-g cryogenic germanium detectors in operation at
the Laboratoire Souterrain de Modane. The combined use of thermal phonon
sensors and charge collection electrodes with an interleaved geometry enables
the efficient rejection of gamma-induced radioactivity as well as near-surface
interactions. A total effective exposure of 384 kg.d has been achieved, mostly
coming from fourteen months of continuous operation. Five nuclear recoil
candidates are observed above 20 keV, while the estimated background is 3.0
events. The result is interpreted in terms of limits on the cross-section of
spin-independent interactions of WIMPs and nucleons. A cross-section of
4.4x10^-8 pb is excluded at 90%CL for a WIMP mass of 85 GeV. New constraints
are also set on models where the WIMP-nucleon scattering is inelastic.Comment: 23 pages, 5 figures; matches published versio
A search for low-mass WIMPs with EDELWEISS-II heat-and-ionization detectors
We report on a search for low-energy (E < 20 keV) WIMP-induced nuclear
recoils using data collected in 2009 - 2010 by EDELWEISS from four germanium
detectors equipped with thermal sensors and an electrode design (ID) which
allows to efficiently reject several sources of background. The data indicate
no evidence for an exponential distribution of low-energy nuclear recoils that
could be attributed to WIMP elastic scattering after an exposure of 113 kg.d.
For WIMPs of mass 10 GeV, the observation of one event in the WIMP search
region results in a 90% CL limit of 1.0x10^-5 pb on the spin-independent
WIMP-nucleon scattering cross-section, which constrains the parameter space
associated with the findings reported by the CoGeNT, DAMA and CRESST
experiments.Comment: PRD rapid communication accepte
Non-contact luminescence lifetime cryothermometry for macromolecular crystallography
Temperature is a very important parameter when aiming to minimize radiation damage to biological samples during experiments that utilise intense ionising radiation. A novel technique for remote, non-contact, in situ monitoring of the protein crystal temperature has been developed for the new I23 beamline at the Diamond Light Source, a facility dedicated to macromolecular crystallography (MX) with long-wavelength X-rays. The temperature is derived from the temperature-dependant decay time constant of luminescence from a minuscule scintillation sensor (<0.05 mm3 ) located in very close proximity to the sample under test. In this work we present the underlying principle of cryogenic luminescence lifetime thermometry, discuss the features of the detection method, the choice of temperature sensor and demonstrate how the temperature monitoring system was integrated within the viewing system of the end-station used for the visualisation of protein crystals. The thermometry system was characterised using a Bi4Ge3O12 (BGO) crystal scintillator that exhibits good responsivity of the decay time constant as function of temperature over a wide range (8 – 270 K). The scintillation sensor was calibrated and the uncertainty of the temperature measurements over the primary operation temperature range of the beamline (30 – 150 K) was assessed to be ±1.6 K. It has been shown that the temperature of the sample holder, measured using the luminescence sensor, agrees well with the expected value. The technique was applied to characterise the thermal performance of different sample mounts that have been used in MX experiments at the I23 beamline. The thickness of the mount is shown to have the greatest impact upon the temperature distribution across the sample mount. Altogether these tests and findings demonstrate the usefulness of the thermometry system in highlighting the challenges that remain to be addressed for the in-vacuum MX experiment to become a reliable and indispensable tool for structural biology
Performance of scintillation materials at cryogenic temperatures
An increasing number of applications of scintillators at low temperatures,
particularly in cryogenic experiments searching for rare events, has motivated
the investigation of scintillation properties of materials over a wide
temperature range. This paper provides an overview of the latest results on the
study of luminescence, absorption and scintillation properties of materials
selected for rare event searches so far. These include CaWO4, ZnWO4, CdWO4,
MgWO4, CaMoO4, CdMoO4, Bi4Ge3O12, CaF2, MgF2, ZnSe and AL2O3-Ti. We discuss the
progress achieved in research and development of these scintillators, both in
material preparation and in the understanding of scintillation mechanisms, as
well as the underlying physics. To understand the origin of the performance
limitation of self-activated scintillators we employed a semi-empirical model
of conversion of high energy radiation into light and made appropriate
provision for effects of temperature and energy transfer. We conclude that the
low-temperature value of the light yield of some modern scintillators, namely
CaWO4, CdWO4 and Bi4Ge3O12, is close to the theoretical limit. Finally, we
discuss the advantages and limitations of different materials with emphasis on
their application as cryogenic phonon-scintillation detectors (CPSD) in rare
event search experiments
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