M. Pavan

Scintillating double-beta-decay bolometers

We present the results obtained in the development of scintillating double-beta-decay bolometers. Several Mo and Cd based crystals were tested with the bolometric technique. The scintillation light was measured through a second independent bolometer. A 140-g CdWO4 crystal was run in a 417-h live time measurement. Thanks to the scintillation light, the α background is easily discriminated, resulting in zero counts above the 2615-keV γ line of 208Tl. These results, combined with an extreme easy light detector operation, represent the first tangible proof demonstrating the feasibility of this kind of technique.

Performance of ZnMoO4 crystal as cryogenic scintillating bolometer to search for double beta decay of molybdenum

Zinc molybdate (ZnMoO4) single crystals were grown for the first time by the Czochralski method and their luminescence was measured under X-ray excitation in the temperature range 85–400 K. Properties of ZnMoO4 crystal as cryogenic low temperature scintillator were checked for the first time. Radioactive contamination of the ZnMoO4 crystal was estimated as ≤ 0.3 mBq/kg (228Th) and 8 mBq/kg (226Ra). Thanks to the simultaneous measurement of the scintillation light and the phonon signal, the α particles can be discriminated from the γ/β interactions, making this compound extremely promising for the search of neutrinoless Double Beta Decay of 100Mo. We also report on the ability to discriminate the α-induced background without the light measurement, thanks to a different shape of the thermal signal that characterizes γ/β and α particle interactions.

New experimental results on double beta decay of 130Te

New results are presented of a search for double beta decay of Te isotopes carried out, using the bolometric technique, with an array of 20 natural tellurite crystals with a total cryogenic mass of ; 6.8 kilograms. The array has been run at a temperature around 10 mK in the Gran Sasso Underground Laboratory. No evidence has been found for neutrinoless double beta decay of 128 Te and 130 Te and upper limits of 8.6 = 10 22 and 1.44 = 10 23 years, respectively, have been achieved at the 90% confidence level. From the latter we obtain limits on the lepton non-conserving parameters which are the most restrictive ones in direct experiments after those on 76 Ge according to theoretical calculations. Results on two neutrino and majoron mediated decays are also presented and discussed with respect to those obtained for the same nuclei in geochemical experiments. q 2000 Elsevier Science B.V. All rights reserved.

Characterization of ZnSe scintillating bolometers for Double Beta Decay

Abstract ZnSe scintillating bolometers are good candidates for future Double Beta Decay searches, because of the 82Se high Q-value and thanks to the possibility of alpha background rejection on the basis of the scintillation signal. In this paper we report the characteristics and the anomalies observed in an extensive study of these devices. Among them, an unexpected high emission from alpha particles, accompanied with an unusual pattern of the light vs. heat scatter plot. The perspectives for the application of this kind of detectors to search for the Neutrinoless Double Beta Decay of 82Se are presented.

A new search for neutrinoless ββ decay with a thermal detector

Abstract A 334 g TeO2 crystal has been operated at a temperature of around 10 mK for more than one year in a low intrinsic radioactivity dilution refrigerator installed in the Gran Sasso Underground Laboratory. From the spectrum collected in 9234 h of effective running time we improve our limit on neutrinoless double beta decay of 130Te by an order of magnitude with respect to our previous experiment. It is the most stringent on this nucleus and excludes a large contribution of the neutrinoless mode to the rate of double beta decay found in geochemical experiments. Upper limits on the effective neutrino mass and on the contributions of right banded currents are given.

Preliminary results on double beta decay of 130Te with an array of twenty cryogenic detectors

Preliminary results on double beta decay of 130 Te obtained in the first run of an array of twenty cryogenic detectors are presented. The set-up is made with crystals of TeO of 340 grams each corresponding to the largest presently operating 2 cryogenic mass. It was run under a heavy shield in the Gran Sasso Underground Laboratory at a depth of about 3500 m.w.e. By recording the pulses of each detector in anticoincidence with the others a 90% c.l. lower limit of 5.6 = 10 22 years has been obtained on the lifetime for neutrinoless double beta decay of 130 Te in a preliminary test run, corresponding to about one week of effective running time. No evidence is also found for double beta decay to the first excited 2 q state of 130 Xe with a 90% c.l. lower limit of 1.7 = 10 22 years on that lifetime. Some consequences of the present results in the

The programmable front-end readout system for Cuoricino, an array of large mass bolometers

We report on the front-end electronics realized for the readout of the CUORICINO experiments array of 60 large-mass bolometers. The front end consists of a preamplifier and a bias system for the bolometer. A second stage completes the analog circuitry. A significant feature of our design is its capability for in-situ DC characterization of each bolometer as a function of applied bias. The principal front-end operating parameters, including low-noise bias selection, load resistor selection, offset compensation, and gain, are remotely programmable.

Monte Carlo evaluation of the external gamma, neutron and muon induced background sources in the CUORE experiment

CUORE is a 1 ton scale cryogenic experiment aiming at the measurement of the Majorana mass of the electron neutrino. The detector is an array of 988 TeO2 bolometers used for a calorimetric detection of the two electrons emitted in the ββ(0ν) of Te. The sensitivity of the experiment to the lowest Majorana mass is determined by the rate of background events that can mimic a ββ(0ν). In this paper we investigate the contribution of external sources i.e. environmental gammas, neutrons and cosmic ray muons to the CUORE background and show that the shielding setup designed for CUORE guarantees a reduction of this external background down to a level < 10 counts/kgkeVyr at the Q-value, as required by the physical goal of the experiment.

New limit on the neutrinoless betabeta decay of 130Te.

We report the present results of CUORICINO, a search for neutrinoless double-beta (0nu betabeta) decay of 130Te. The detector is an array of 62 TeO2 bolometers with a total active mass of 40.7 kg. The array is cooled by a dilution refrigerator shielded from environmental radioactivity and energetic neutrons, operated at approximately 8 mK in the Gran Sasso Underground Laboratory. No evidence for (0nu betabeta) decay was found and a new lower limit, T(1/2)(0nu) > or = 1.8 x 10(24) yr (90% C.L.) is set, corresponding to [m(nu)] < or = 0.2 to 1.1 eV, depending on the theoretical nuclear matrix elements used in the analysis.

A massive thermal detector for alpha and gamma spectroscopy

A massive bolometer with a 760 g TeO2 crystal as energy absorber, the largest employed underground, has been realized and operated in the Gran Sasso Underground Laboratory for γ- and α-ray spectroscopy. A new system of mechanical suspensions was implemented to reduce vibration and thermal noise, and special care was put to the read-out electronics. As a consequence the FWHM resolution for high-energy γ-rays became comparable to that of Germanium diodes. The 4.2 keV average FWHM resolution for the 5407 keV line is the best ever obtained for α particles with any type of detector.