[en] The author reviews his contributions to the use of bolometers (cryogenic detectors) for the detection of wimps (weakly interactive massive particles). Wimps are detected through their elastic scattering on the nuclei of the detector, a heat signal, luminescence or ionization can be simultaneously detected (at least 2 signals are necessary to discard photon interactions). Bolometers operate at low temperatures (< 50 mK) so they allow very low detection threshold and resolution (< keV) with a full energy conversion for recoiling nuclei. In Saclay the technology of bolometers based on simultaneous detection of heat and ionisation has been developed and improvements have been studied (NbSi thin films bolometers). The first results obtained in the framework of the Edelweiss collaboration are presented. Other developments based on infra-red bolometry (Planck surveyor and Archeops projects) are briefly described. In an appendix the operating principle of a bolometer is presented. (A.C.)

[en] We implemented a low noise current preamplifier for the readout of resistive bolometers. We tested the apparatus on thermometer resistances ranging from 10 to 500 MΩ. The use of current preamplifier overcomes constraints introduced by the readout time constant due to the thermometer resistance and the input capacitance. Using cold JFETs, this preamplifier board is shown to have very low noise: the Johnson noise of the source resistor (1 fA/Hz^1/2) dominated in our noise measurements. We also implemented a lock-in chain using this preamplifier. Due to fast risetime, compensation of the phase shift may be unnecessary. If implemented, no tuning is necessary when the sensor impedance changes. Transients are very short, and thus low-passing or sampling of the signal is simplified. In case of spurious noise, the modulation frequency can be chosen in a much wider frequency range, without requiring a new calibration of the apparatus

[en] In this paper, the authors present new results from a cryogenic detector instrumented to measure both the phonon and ionization signals. The detector is a 60 g Ge disk operated at 30 mK. The authors have made significant improvements in the electronics noise, threshold, and energy resolution of the device. The baseline FWHM, corresponding to the total system noise, is 1.55 keV in the phonon channel and 1.59 keV in the ionization channel. At 60 keV the FWHM are 1.9 keV and 1.7 keV in the phonon and ionization channels, respectively. The authors have demonstrated for the first time a discrimination between electron recoils and nuclear recoils at low energy

[en] In this paper we present two configurations of innovative gamma detectors using Cherenkov light for time-of-flight—Positron Emission Tomography (PET). The first uses heavy crystals as a Cherenkov radiator to develop a demonstrator for a whole body PET scanner with high detection efficiency. We demonstrated a 30% detection efficiency and a 180 ps (FWHM) time resolution, mainly limited by the time transit spread of the photomultiplier. The second configuration uses an innovative liquid, the TriMethyl Bismuth, to develop a high precision brain-scanning PET device with time-of-flight capability. According to Geant4 simulation, we expect to reach a precision of 150 ps (FWHM) and an efficiency of about 25%.

[en] We study the possibility to use the Cherenkov light for the efficient detection of 511 keV photons with the goal to use it in TOF-PET . We designed and tested two detection modules consisting of PbF₂ crystals attached to Planacon MCP-PMT XP85012. Amplified PMT signals are digitized by the SAMPIC module with high readout rate, up to 10⁵ events/s, and a negligible contribution to the time resolution, below 20 ps (FWHM) . We developed a fast 2D scanning system to calibrate the PMT time response and studied in details the timing characteristics of the Planacon PMT. Using a radioactive ²²Na source we measured a detection efficiency of 24% for 511 keV photons in a 10 mm thick crystal and a coincidence resolving time of 280 ps. We analyzed the main factors limiting the time resolution of the large-surface detection module and proposed solutions to improve it, which will be tested in our future project.

[en] In the context of the ClearMind project, we measured the scintillating properties, as induced from gamma ray interactions, of today available PbWO₄ crystal. We measured scintillation's yields and time constants by measuring the signal shape measured on a fast photo-multiplier and deconvoluting it from the instrumental effects. For the doped crystals at room temperature, we measured a fast scintillation component, with time constants of 2 ns, 55 % of the total light yield, and a slow component of 6 ns. We observe a significant increase of the light yield for the slow component when the temperature decreases and simultaneous increase of the time constants, but no increase in the fast component light yield. Our measurements reproduce the main qualitative features of PbWO₄ crystals quoted in the literature. Quantitatively though, we measured significantly shorter time constants and larger light yields. This is explained by a rigorous treatment of the instrumental contributions in the measurements. Results are discussed and prospect for future developments “tailored” for the ClearMind project are presented. (paper)

[en] The status of the EDELWEISS experiment (underground dark matter search with heat-ionisation bolometers) is reviewed. Auspicious results achieved with a prototype 70 g Ge heat-ionisation detector under a 2 V reverse bias tension are discussed. Based on gamma and neutron calibrations, a best-case rejection factor, over the 15-45 keV range, of 99.7% for gammas, with an acceptance of 94% for neutrons, is presented first. Some operational results of physical interest obtained under poor low radioactivity conditions follow. They include a raw event rate of around 30 events/day/kg/keV over the same energy range, and, after rejection of part of the background, lead to a conservative upper limit on the signal of approximately 1.6 events/day/kg/keV at a 90% confidence level. Performance degrading surface effects of the detector are speculated upon; and planned upgrades are summarized

[en] The CaLIPSO project focuses on the development of an innovative energetic-photon detector. The detector uses a 'heavy' organometallic liquid: the Trimethyl Bismuth (TMBi), 82% by weight of Bismuth. TMBi efficiently converts through the photo-electric effect photons of energies below 1 MeV. The ionisation signal and light produced in the liquid are both detected. Beyond the measurement of gamma photon energies, this detector will allow locating photon interactions in the detector in three dimensions down to 1 mm³ and a sub nanosecond timing accuracy. All these desirable properties can be obtained simultaneously with liquid TMBi detector. The optical properties relevant for particle detection are measured. Preliminary results on TMBi ionization properties are shown. (authors)

[en] This issue is dedicated to the 20. anniversary of the creation of the IRFU institute that gathers the research activities of CEA on physics. About 20 short articles present in a very pedagogical manner the various contributions of IRFU to the understanding of modern physics, it concerns neutrinos, dark matter, matter/anti-matter asymmetry, nucleon sub-structure, nuclear structure and the structure of the universe

[en] We describe the concept of a new gamma ray "scintronic" detector targeting a time resolution of the order of 25 ps FWHM, with millimetric volume reconstruction and high detection efficiency. Its design consists of a monolithic large PbWO${}_4$ scintillating crystal with an efficient photocathode directly deposited on it. With an index of refraction higher for the photocathode than for the crystal, this design negates the total reflection effect of optical photons at the crystal/photo-detector optical interface, and thus largely improves optical coupling between the crystal and the photodetector. This allows to detect efficiently the Cherenkov light produced by 511 keV photoelectric conversions in PbWO${}_4$, and to optimize the detector time resolution. Furthermore, the low-yield, fast scintillation light produced additionally by PbWO${}_4$ increases the detected photon statistics by a factor 10, thus fostering accurate (3 dimensional) localization of the gamma ray interaction within the crystal and providing a fair measurement of the deposited energy. This paper lists the technological challenges that have to be overcome in order to build this "scintronic" detector. We show that all the key technologies have now been demonstrated and present results of a preliminary Monte Carlo simulation, which include an innovative event reconstruction algorithm to support the claimed performances of the detector.