[en] The composite bolometer with monolithic doped germanium thermistor is a good approach towards the ideal thermal spectrometer. We have measured the thermal parameters of heavily doped germanium that are required to optimize the thermal coupling between substrate and sensor. Sensors in the megohm range are obtained by high precision resistivity tests and pre-selection at 300K. Heat capacity corresponding to 2 eV resolution has been measured at 40 mK. We have tested with success several bolometers with mass from 1 mg to 25 g. Best FWHM resolutions obtained are 29 KeV on α's, 2 KeV on e^-'s and 300 eV on γ's. These results are obtained by filtering extraneous sources of energy like microphonics. We have reached a resultuion of 16 KeV on a γ line with a 25 gram sapphire composite bolometer at 0.1K which is the largest and most massive bolometer ever successfully tested; it confirma the promising possibilities of bolometers for dark matter particles detection. (author). 30 refs.; 14 figs

[en] A 334g TeO₂ crystal is operating since January '93 at Gran Sasso National Laboratories as a thermal detector to search for neutrinoless ββ decay of ¹³⁰Te. The reduction of environmental radioactivity is accomplished by means of a 10 cm thick external lead shielding and a plexiglas box against ²²²Rn, while an inner ultra-low activity lead shield of at least 3.5 cm in every direction suppresses the residual local radioactivity near the crystal. The good energy resolution and the peak-to-Compton efficiency of the detector allow to understand the main features of the residual background. In particular, the authors are able to reach a sensitivity in the internal contamination of ²³⁸U and ²³²Th of the crystal of the order of 10^-13 g/g, better than that of modern mass spectroscopy methods. Pulse acquisition and analysis techniques are reported and discussed. Present limit on neutrinoless ββ decay half-life time of ¹³⁰Te obtained with this detector is of the order of 10²²y at 68% C.L., exceeding by one order of magnitude the value quoted by the inclusive geochemical measurements, which have therefore to be attributed mainly to the 2-neutrino channel

[en] The ROSEBUD collaboration measured the differential flux of fast neutrons inside a shielding of lead irradiated with a source of ²⁵²Cf using two scintillating bolometers of LiF and Al₂O₃ at 20 mK. We compare an unfolding method using a three parameter model for the fast component of the neutron flux with a multigroup method in which the energy interval of interest is divided into groups. Some issues regarding the neutron monitoring with LiF or Al₂O₃ in a cryogenic experiment searching for dark matter WIMPs are discussed.

[en] On account of its qualities for dark matter research, a 300 mg luminescent CaF₂(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 CaF₂(Eu) targets of several grams and lower working temperatures. (orig.)

[en] A 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 rate and difficult to cool down. We have developed a specially designed compact X-ray source where ⁵⁵Fe is combined with an ion-exchange 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. (orig.)

[en] Neutrons are a relevant background in rare events physics. Detectors based on fast neutron-induced nuclear reactions are commonly used for fast neutron spectroscopy. In this subject, scintillating bolometers provide an excellent energy resolution and particle discrimination by the simultaneous measurement of the heat and emitted light. Our group has constructed several ⁶Li and ¹⁰B based massive scintillating bolometers (LiF, Li₆Eu(BO₃)₃, Li₆Gd(BO₃)₃), with energy resolutions ranging from 16 to 200 keV. First results of a 32 gr ⁶LiF scintillating bolometer enriched at 95% in ⁶Li operated at 20 mK are presented. The use of this material in a multi-target cryogenic dark matter experiment, like EURECA, would allow monitoring the incident neutron flux in the detector during the data-taking.

[en] The bolometric technique to detect the energy release of charged and uncharged particles inside a crystal absorber has been proposed since long time. Various detectors have been studied and realised in the last years showing the good performances which can be reached with low temperature calorimeters. The application of these types of detectors is particularly interesting to measure the neutrino mass or to search for rare events, such as Double Beta Decay or Dark Matter. In many cases these experiments have to be performed in deep underground locations to be shielded against cosmic rays. Present results, particularly regarding neutrinoless Double Beta Decay search of ¹³⁰Te by the Milano group, and future perspectives are discussed. (orig.)

[en] A new generation of detectors for non-accelerator particle physics has been under development in the last years and has recently started to be used in experimental searches. The results have already demonstrated that low temperature detectors can be competitive with conventional ones in several fields of non-accelerator particle physics. The near future upgrading of this technique will be the extension from one single crystal device to arrays of several single crystals. This new detector set-up poses stimulating and original technical problems, both on detector structure and signal analysis: our progresses in this field are reported. (orig.)

[en] The development of low-threshold detectors for the study of coherent elastic neutrino-nucleus scattering and for the search for light dark matter necessitates methods of low-energy calibration. We suggest this can be provided by the nuclear recoils resulting from the γ emission following thermal neutron capture. In particular, several MeV-scale single-γ transitions induce well-defined nuclear recoil peaks in the 100 eV range. Using the FIFRELIN code, complete schemes of γ-cascades for various isotopes can be predicted with high accuracy to determine the continuous background of nuclear recoils below the calibration peaks. We present a comprehensive experimental concept for the calibration of CaWO₄ and Ge cryogenic detectors at a research reactor. For CaWO₄ the simulations show that two nuclear recoil peaks at 112.5 eV and 160.3 eV should be visible above background simply in the spectrum of the cryogenic detector. Then we discuss how the additional tagging for the associated γ increases the sensitivity of the method and extends its application to a wider energy range and to Ge cryogenic detectors. (paper)

[en] 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 Po electrodeposited source was made for the first time with the use of a 2 mm³ 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. ((orig.))