A. Alessandrello

Cryogenic voltage-sensitive preamplifier using GaAs MESFETs of low 1ƒ noise

Abstract A voltage-sensitive preamplifier using GaAs MESFETs of low 1 ƒ noise has been developed. The voltage gain is fixed to 51. With a total power dissipation of 54 mW the preamplifiers series noise level at 4 K is 9 nV / Hz 1 2 at 100 Hz and 0.3 nV / Hz 1 2 at 100 kHz. The input bias current of the preamplifier was determined to be lower than 10 fA below 100 K. Response to a step pulse gave a rise time of 40 ns when loaded with a 130 pF load. The voltage-sensitive preamplifier is presently used in Milano for signal readout and characterization of large-mass bolometric particle detectors. An energy resolution of 13 keV for the 1330 keV of a 60Co gamma source was obtained with an 11 g Ge bolometric detector readout with this preamplifier.

Heat Capacity of a Silicon Calorimeter at Low Temperatures Measured by Alpha-Particles

A small implanted monolithic silicon calorimeter has been bombarded with alphaparticles at low temperatures in order to determine its thermal properties. From the temperature dependence of the pulse height and the time structure, we have obtained values for the lattice contribution to the heat capacity in excellent agreement with theory, while the contributions from the implanted zone are about an order of magnitude larger than expected from data on diffusion-doped semiconductor. This and other thermal properties are discussed.

Gallium-arsenide charge-sensitive preamplifier for operation in a wide low-temperature range

A charge-sensitive preamplifier for temperature operation between 1 and 120 K has been developed and evaluated. It uses double-gate GaAs MESFETs selected for their low 1/ƒ noise. These devices are operated with both gates interconnected emulating single-gate MESFETs of double gate-length, obtaining in this way a value for Aƒ, the coefficient of the 1/ƒ noise spectral power density, of 1.7 × 10−13 V2 at 77 K and 3.8 × 10−14 V2 at 4 K. The latter is one fourth the value exhibited by the original device before modification and two orders of magnitude less than the value measured at 300 K. At the optimum bias operating point device transconductance is 6 mA/V, input capacitance is less than 5 pF and the power dissipation 360 μW. The circuit configuration consists of a double-cascade loaded with a bootstrapped current source. In this way, a high gain-bandwidth product is obtained despite of the low dynamic output resistance, 3000 Ω, exhibited by the MESFETs at the operating point. Equivalent noise charge was measured for detector capacitances up to 35 pF. Using a semi-Gaussian weighting function minimum values of 58 and 20 rmse− at 77 and 4 K, respectively, were determined. Noise slopes are 4.68 and 3.64 e−/pF at 1 μs shaping time for 77 and 4 K, respectively. A rise time of 20 ns was measured at the receiving-end of a 1 m length 50 Ω coaxial cable terminated at sending-end, when detector capacitance was CD = 35 pF. The total power dissipation of the preamplifier is less than 10 mW.

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.

Thermal detection of particles using bolometric devices

Abstract Low temperature calorimeters can be used to measure the energy released by a single particle with very high resolution. We have developed a system for studying the behaviour of various kinds of calorimeters from the point of view of their thermoelectrical properties and also their characteristics as particle detectors. Preliminary experimental results of a composite detector are shown (the resolution is 3% for the 8.78 MeV α-line from 228 Ra). Future developments both for optimizing the resolution and improving the system performances are briefly discussed.

Heat Capacity of P-Doped Si Thermistors at Low and Very Low Temperature Measured by Alpha-Particles and X-Rays

The heat capacities of three specially implanted silicon bolometers have been measured at low and, for the first time, at very low temperatures down to about 10 mK by exposing them to alpha-particles and X-rays. The lattice contribution shows a behaviour with temperature in good agreement with the Debye law, and the percentage of thermalized energy of the alpha-particle is found to be about 70%. The specific heat of the doped part, which dominates at very low temperatures, is not inconsistent with linearity, even if a dependence on a higher power of the temperature seems preferred. The parameter of linearity is found to be considerably larger than expected from extrapolation to very low temperatures of the existing results on silicon P-doped by diffusion.

Considerations on Front End Electronics for Bolometric Detectors with Resistive Readout

We have started some time ago a research activity to evaluate the possible use of cryogenic detectors in the detection of very rare events [1]- First tests of silicon calorimeters have been performed at CERN and showed the feasibility of using such devices as photon detectors- Germanium, totally doped commercial thermometers have been also used as detectors for alpha particles [2], [3]. In collaboration with SGS, the main local semiconductor manufacture, we are currently developing a series of silicon cryogenic detectors which will be tested with low-energy photons emitted by a 55Fe X-ray source.

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.