Large Mass Bolometers for neutrinoless Double Beta Decay detection: Model and last results

Year: 2004

Authors: Pedretti M., Barucci M., Giuliani A., Pasca E., Risegari L., Olivieri E., Ventura G.

Autors Affiliation: Universitą dell\’Insubria, via Valleggio 11, 22100 Como, Italy; Dipartimento di Fisica, Universitą di Firenze, Via Sansone 1, 50019 Sesto Fiorentino (FI), Italy

Abstract: Milano collaboration has been developing for many years large mass bolometers for particle detection, and in particular for the study of neutrinoless Double Beta Decay of 130Te. The active components of the detectors are large mass (340 g and 790 g) TeO2 crystals, while Neutron Transmutation Doped Ge thermistors are used as phonon sensors. These devices work at low temperatures, about 5-10 mK. The mechanical and thermal connections of the detector to the thermal bath are made with PTFE pieces that hold the crystal on copper frames. Gold wires are used as electric connections. We have developed a complete thermal model for the bolometers and \”ad hoc\” measurements of the thermal parameters involved were performed in the Florence cryogenic laboratory. These studies have permitted to simulate the static and dynamic behaviors of the detectors. A satisfactory agreement between the simulated and the experimental response has been obtained as far as the static behavior is concerned, while the dynamic behavior is not yet fully understood. These preliminary results however will enable us to design new detector structures in order to improve the signal-to-noise ratio and the reproducibility. Given the good performances of these devices (excellent energy resolutions were obtained, of the order of 2 keV at 911 keV and of 5 keV at 2615 keV), this technique is particularly suitable to detectors for gamma ray spectroscopy. Encouraged by this results, the Milano-Como group has joined a large international collaboration for the realization of CUORE (Cryogenic Underground Observatory for Rare Events), searching for Dark Matter and neutrinoless Double Beta Decay, a crucial phenomenon for neutrino physics. The Cuoricino detector, a small scale test of CUORE detector, is an array of 62 large mass bolometers like those already described, and it is now in operation in the Gran Sasso underground laboratory (Italy). It is the largest array of bolometric detectors ever constructed.

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KeyWords: Bolometers; Capacitance; Computer simulation; Doping (additives); Gamma rays; Gold; Low temperature effects; Phonons; Sensitivity analysis; Signal to noise ratio; Spectroscopic analysis; Tellurium compounds; Thermistors, Bolometric detector; Detector simulation; Gamma ray detectors; Low temperature detectors; Thermal models, Radiation detectors
DOI: 10.1117/12.505231