O. Cremonesi

A Search for Double Beta Decay of 128Te and 130Te Leading to the First Excited State of Daughter Nuclei

A shielded Ge(Li) surrounded by natural tellurium and located in an underground laboratory has been used to search for double beta decay of 128Te and 130Te leading to the first 2+ excited state of the corresponding Xenon isotopes. No evidence for such decays is found and it is proved experimentally that the geologically measured rate for double beta decay of 130Te is dominated by the 0+-0+ mechanism. Upper limits on the presence of right-handed currents are obtained which are independent of the value for the neutrino mass.

A programmable front-end system for arrays of bolometers

We report on a new front-end system developed to readout an array of large mass bolometers. The front-end allows setting all the necessary parameters for each detector by remote control. A special circuit, also red remotely, has been developed in order to adjust the output voltage, allowing the DC coupling to the detector. ( 2000 Elsevier Science B.V. All rights reserved.

A front-end for an array of /spl mu/-bolometers for the study of the neutrino mass

We present a very low noise front-end solution for the readout of an array composed of 10 /spl mu/-bolometers. The system consists of a cold JFET and a room temperature second stage. The optimization of the second stage feedback configuration allowed to minimize the overall noise figure. A very simple current generator having a large output impedance has been developed and is used for biasing the cold JFET.

Signal modelling for TeO2 bolometric detectors

An energetic particle impinging a large mass bolometric detector generates signals of different shape depending on where the energy is deposited: in the absorber or in thethermal sensor. By exploiting this effect and the thermal characteristic of the sensor, all the parameters needed for simulating the dynamic behaviour of the detector for small and large signals were extracted. The model was used for simulating a series of 3 TeO2 bolometers with mass of 70g and 330g. For an accurate analysis an electric field effect dependance of the electron-phonon thermal conductance and electrons heat capacity in the thermistors used was taken into account. Also an interesting measured and simulated effect was considered regarding the quasi complete thermalized energy given by an α-particle.

Multielement Proportional Chamber for 136Xe ββ decay

Abstract A Multielement Proportional Chamber designed to investigate ββ decay of 136 Xe is described. The detector consists of 61 cells. arranged in a honeycomb structure. Each cell is 80 cm long and has a hexagonal cross section of 2.5 cm side. The anodes are 20 μm diameter gold plated tungsten wires. Each cathode consists of 24 copper-beryllium wires of 100 μm diameter. This structure is mounted in a titanium vessel of 40 cm diameter and 110 cm length. In order to obtain a very low background all the materials used were selected for their low intrinsic activities. The detector is operated with Xe at 10 bar; a purification system keeps the oxygen like impurities below 0.2 ppm. The electronics consists of 61 hybrid charge sensitive preamplifiers followed by 7 bit CAMAC flash-ADCs to digitize and store the pulses. An auxiliary output of the preamplifier is used to drive a trigger module that can be preset to any configuration of total energy and/or anode pattern. The chamber, presently under test, will soon be installed in the Gran Sasso underground Laboratory for data taking. Measurements on energy resolution over several cells and on charge transport are described.

A linear, low-noise, low-power optocoupler amplifier for bolometric detectors

We present an optocoupler with di⁄erential inputs and balanced output, which was realized to make galvanic decoupling in a bolometric detector read-out chain. The circuit configuration incorporates a true di⁄erential optocoupled feedback, with low bias current in LEDs and photodiodes. Large Common Mode (CMRR) and Power Supply (PSRR) Rejection Ratio, low crossover distortion, high dynamic range, low noise and power dissipation have been achieved. ( 1998 Elsevier Science B.V. All rights reserved.

Measuring thermistor resistance with very low d.c. power dissipation

Abstract A very simple and efficient procedure for measuring thermistor resistances at very low temperatures (down to 5 mK) with d.c. bias voltages is presented. The measurements can be performed with a d.c. power dissipation in the thermistors as low as 10 −18 W or less, as required by the extreme thermistor sensitivity to small heating effects. In particular this method suppresses the effects of the input current of the amplifier used for the measurement. We are using this procedure for the automatic characterization of thermistors with impedances up to 10 9 Ω at temperatures as low as 10 mK.

Cryogenic, monolithic, differential GaAs preamplifier for bolometric detectors

Abstract We present a first prototype of a monolithic differential voltage-sensitive preamplifier for cryogenic applications made in a GaAs ion implanted MESFET process. This preamplifier presents a very high input impedance using only a single long-tailed pair at its input, which allows the noise to be kept low. It was designed to obtain low power dissipation and a large dynamic range. The results of the first prototype chips are presented.

Gamma ray spectroscopy with high-Z thermal detectors

Abstract A massive thermal detector to be used to search for rare decays and to detect high-energy γ-rays has been operated both at sea level and underground. It consists of a 20.9 g monocrystal of TeO 2 whose temperature is measured by means of a neutron transmutation doped thermistor. The detector was first operated in Milano at a base bolometer temperature of 22.5 mK and with a FWHM resolution of 90 keV, rather independent of the γ-ray energy. Much better results have been obtained when the detector was operated underground, under a suitable shielding against local radioactivity and inside a Faraday cage. The base bolometer temperature could be as low as 14.5 mK which, together with the elimination of pile-up, allowed to achieve FWHM resolutions of 1% for γ-rays above 2.0 MeV. The increase in the base temperature of the bolometer when exposed to a weak radioactive source is discussed in view of possible applications in the search for dark matter.

The Mont Blanc experiment on 76Ge double beta decay

An experiment on neutrinoless double beta decay of 76Ge to the ground and first excited state of 76Se is in progress in the Mont Blanc Laboratory at a depth of ∼5000 m w.e. of rock. A measurement of more than 6800 hours allows to set limit of ∼5.1022 yrs (1σ) and 4.5 1021 yrs (1σ) respectively on O+→O+ and O+→2+ neutrinoless ββ transitions of 76Ge to 76Seg.s and 76Se(2+,559 keV).