N. Coron

ALPHA/GAMMA DISCRIMINATION WITH A CAF2(EU) TARGET BOLOMETER OPTICALLY COUPLED TO A COMPOSITE INFRARED BOLOMETER

Abstract On account of its qualities for dark matter research, a 300 mg luminescent CaF 2 (Eu) bolometer light-coupled to an infrared sapphire bolometer has been successfully investigated. At a working temperature of about 130 mK, a discrimination between alpha particles and gamma irradiation has been achieved. The rejection power as a function of energy is given. We finally discuss an extrapolation of our results to CaF 2 (Eu) targets of several grams and lower working temperatures.

Dark matter search with a low temperature sapphire bolometer

Abstract A dark matter detection experiment using a low temperature 24 g sapphire bolometer is presented. The low radioactive background cryogenic facility, installed in a deep underground site, is described, as well as the low-noise read-out electronics and the data analysis. From the energy spectrum, measured down to 4 keV, exclusion plots are derived for WIMPs having coherent vector coupling or axial coupling to ordinary matter.

Bolometric detection of the recoil spectrum in the alpha decay of 210Po

Abstract Bolometers at low temperature are being developed as particle spectrometers and potential detectors of dark matter particles through the measurement of recoil energies. A successful observation of the recoil spectrum from a 210 Po electrodeposited source was made for the first time with the use of a 2 mm 3 composite-composite diamond bolometer operated in a 300 mK cryostat. The measured recoil ratio is 0.98±0.06 recoil/alpha above 50 keV, with the well defined peak in the spectrum at 101±2.5 keV.

Characterization of a 2 g LiF bolometer

Abstract The bolometric properties of a 2 g LiF single crystal have been investigated below 100 mK under alpha and thermal neutron irradiation. The reported energy resolution at 5 MeV on both alphas and the neutron capture line of the n( 6 Li, α)t reaction is 16 keV FWHM. Evidence is given for a dependence of the thermal response on the nature of the absorbed radiation. Light emission of undoped LiF has been investigated down to 10 K under gamma and alpha irradiation. We discuss the possibility to use LiF bolometers in dark matter detection experiments and neutron spectrometry.

Enhanced performance of a bolometric detector at mK temperatures in high magnetic fields

Results on the operation of a bolometer detector in high magnetic fields and at very low temperatures are presented. We tested a diamond absorber on a Ge thermistor in magnetic fields up to 8 Tesla and temperatures down to 10 mK using an55Fe X-ray and109Cd electron source. Heavily doped Ge shows a giant magnetoresistance effect. This was used to tune the thermistor impedance to an optimal value.

Calorimetric single particle detection in high magnetic fields at low temperatures

High resolution calorimetric detection of single particles in magnetic fields up to 8 T at temperatures <0.1 K is reported. A careful study of heavily doped Si and Ge thermistors reveals an extremely large positive magnetoresistance in the variable range hopping conductivity regime. This phenomenon is used to optimize the impedance and the temperature sensitivity of a calorimetric detector. Initial experiments show an energy resolution full width at half maximum of 800 eV for 62.5 keV conversion electrons and an energy threshold of <400 eV.

First results of the EDELWEISS experiment

The ethical question about the information technologies We refer here to Aristotles definition of ethics to illuminate some practices generated by information technology. For example, the accumulation of documents (temptation to “possess” resources ), the problem of incorporating user – generated information within the project phases (problem of integrating alternative approaches), the assertion about the absolute freedom to make use of the ideas accessible on the web (the individuals interest takes precedence over laws of property); the decisive significance imputed to knowledge as opposed to imagination or affectivity. The denial of the corporeal in the world of the intellect is a philosophical point of view with its roots deep in gnosticism.

Bolometer characterisation with a specially developed cryogenic source having more than five peaks in the 1–6 keV range

At very low temperature (10–50 mK), and at relatively low energy (typically 100 eV–10 keV), the linearity and resolution of bolometers need to be carefully tested. Commercially available sources below 6 keV are rare and difficult to cool down. We have developed a specially designed compact X-ray source where 55Fe is combined with an ion-exchanged membrane containing more than three fluorescent elements. More than five peaks can be identified form 1 keV to 6.5 keV. A spectrum obtained with a 0.5 mg composite diamond bolometer, allowing a good measurement of linearity and resolution as a function of energy is presented. It is compared with a spectrum of the same source measured with a classical germanium detector. Since bolometer detectors have neither window, nor dead layer effects, bolometer spectra obtained with these sources could be used to directly calibrate the efficiency response of classical detectors at very low energy.