D.V. Camin

A scintillating bolometer for experiments on double beta decay

Abstract The scintillation yields of CaF 2 crystals with different doping concentration of Europium have been measured at low temperatures and their bolometric behavior has been investigated. After these studies we have constructed the first “scintillating bolometer” where the heat and scintillation pulses produced by charged particles are simultaneously recorded. With this method a strong suppression of the background from α -particles in the energy region of interest for searches on double beta decay of 48 Ca can be achieved.

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.

The thermal detection efficiency for recoils induced by low energy nuclear reactions, neutrinos or weakly interacting massive particles

Abstract We report the first direct measurements on the energy dependence of the thermal detection efficiency for heavy recoiling nuclei. Two bolometers made by TeO 2 crystals facing each other were operated at low temperature and read-out independently, while coincidence-anticoincidence techniques were used for particle discrimination. The experiment was carried out underground after implantation of both crystals with a source of 228 Ra. The relative response for alpha particles and nuclear recoils with respect to electrons of the same energy (Quenching Factor) was found to be compatible with or slightly larger than unity. Deviations from constancy with energy of the QF for nuclear recoils in α decays of 224 Ra, 220 Rn, 216 Po, 212 Po and 212 Bi were not observed.

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

Construction of a massive germanium thermal detector for experiments of rare decays

Abstract In view of future experiments on rare decays we have constructed and operated a composite germanium bolometer with an energy resolution of about 1% and a mass of about 0.7g, larger by more than three orders of magnitude than those of any existing thermal detector. Unlike the previous ones, this bolometer also present heat capacity in good agreement with the Debye law, with a percentage of thermalized alpha particle energy of at least 70%.

Low frequency noise versus temperature spectroscopy of recently designed Ge JFETs

During the investigation of cryogenic properties of recently developed Ge JFETs we have applied the technique known in literature as low frequency noise versus temperature spectroscopy (LFN versus T). Using this method we have determined the energy levels of traps associated to Lorentzian noise found in the 30 to 40 K temperature range. To perform this task we have developed a computer-controlled experimental setup able to set the temperature within /spl plusmn/5 mK in the range 4 to 300 K during a spectral noise measurement. An approach for the calculation of the uncertainties that affect the evaluation of traps parameter is presented.

A search for neutrinoless double beta decay of 130Te with a thermal detector

Abstract A 73.1 g TeO2 bolometric detector has been operating for more than two months at about 16 mK in a specially constructed low activity dilution refrigerator installed in the Gran Sasso Underground Laboratory and shielded against environmental radioactivity. Its energy resolution is comparable with that of a Ge diode. A spectrum of the thermal pulses collected in 1389 h of effective running time shows no evidence for neutrinoless double beta decay of 130Te. The corresponding lower limit of the lifetime is three orders of magnitude more stringent than those obtained for the some nucleus with conventional techniques. It also exceeds the value for the inclusive (two neutrino and neutrinoless) lifetime obtained by geochemical searches. Double beta decay of 130Te has therefore to be attributed mainly to the two neutrino channel.

Development of a thermal scintillating detector for double beta decay of 48Ca

Abstract Among double beta candidates 48Ca stands out for its 4.271 MeV transition energy, well above most of the contribution of natural γ and β radioactivity, but extremely near to the energy released in the α decay of 238U (4.274 MeV including nucleus recoil). A CaF2(Eu) detector with both thermal pulse and scintillation light readout would give very good discrimination against this very dangerous source of background. We tested CaF2 crystals with 0.01 to 0.07% Eu doping, in the range of temperature between 300 K and 20 mK. The result shows that detection of the scintillation light from alpha particles of 5.4 MeV with a silicon photodiode is possible down to 20 mK with high signal/noise ratio, and that such doping levels do not affect the performance of CaF2 as a thermal detector

Preliminary results on the performance of a TeO2 thermal detector in a search for direct interactions of WIMPS

Abstract During a Double Beta Decay experiment performed at Laboratori Nazionali del Gran Sasso, a 1548 hours background spectrum was collected with a 340 g TeO2 thermal detector. An analysis of this spectrum has been carried out to search for possible WIMP signals. The values for parameters which are essential in the search for WIMPs, like energy resolution (2 keV), energy threshold (13 keV) and nuclear recoil quenching factor (≥ 0.93) have been experimentally determined and are discussed in detail. The spectrum of recoils induced by α decays has been directly observed for the first time in coincidence with the α particle pulse. Preliminary limits on the spin-independent cross sections of WIMPs on Te and O nuclei have been obtained.

The analog signal processor of the Auger fluorescence detector prototype

The Auger Fluorescence Detector will allow to determine the longitudinal development of atmospheric showers in the range 10 19 –10 21 eV. A detector module comprises an array of 20 � 22 PMTs at the focal surface of a large-aperture telescope. Thirty such modules will be used. The PMTs pixel signal is variable in shape depending on the shower-eye geometry. The sky background light (BL) is also variable. We have developed an analog signal processor to obtain best energy and timing resolution despite those constrains. The Head Electronics (HE) bias the PMTs and keeps its pulsegain constant even for large BL. This is measured using a current-monitor of novel design. Both the signal pulse and the BL DC level are sent via a single twisted pair to the Analog Board (AB). The AB performs the compression of the 15–16 bit signal dynamic range into 12 bits of the FADC which follows the AB. A three-pole Bessel filter was adopted for antialiasing. The AB includes 16 bit sigma-delta chips to readout the BL DC level, and a test-pulse distribution system. # 2001 Elsevier Science B.V. All rights reserved. PACS: 29.40