C. Boiano

Wide-dynamic-range fast preamplifier for pulse shape analysis of signals from high-capacitance detectors

A new hybrid charge-sensitive preamplifier with a sensitivity of 5 mV/MeV has been specifically designed to operate in conjunction with high-capacitance silicon detectors. The shape of the leading edge of its impulse response remains fast (20 ns) and unchanged over the full output voltage range (7 V), as is required in nuclear-physics experiments in which pulse-shape analysis is used for particle identification. The circuit is miniaturized onto two sides of a ceramic substrate as small as 17/spl times/23 mm/sup 2/. A low-noise fast discharge technique is used: the return to the high-value feedback resistor (R/sub F/) comes from a noninverting low-gain (A) amplifier cascaded to the principal charge-amplifier loop. This yields a reduction of the fall time of a factor A, with no changes of C/sub F/ and R/sub F/ and no added noise. The shorter fall time reduces the pileup effects in presence of high event rates. Special care has been devoted to the matching between the high capacitance of the detector and that of the input stage of the preamplifier. To match a high capacitance, four BF862 field-effect transistors have been connected in parallel.

Resistive or capacitive charge-division readout for position-sensitive detectors

Two-point charge division is a typical technique for position measurements in linear multi electrode detectors (microstrips, multiwire proportional counters, silicon drift-detector arrays, and scintillators coupled to photodetectors). Only two preamplifiers, located at the right and the left ends of the detection array, are used, each of which receives a fraction of the charge produced by the ionizing event. Position is reconstructed comparing these charge fractions. In principle, either a resistive or a capacitive divider may be used to split the charge. The choice between such two different setups is not obvious. In fact, each of them shows advantages and disadvantages in terms of noise, signal propagation, and linearity. In this paper, we present a unified treatment for the capacitive and the resistive mechanisms of charge division that addresses the issues of this choice. As an example, the realistic setup of the multiwire position-sensitive proportional counter to be used in the TP-MUSIC III chamber of the ALADiN experiment at GSI is considered.

Particle identification via pulse shape analysis for large-area silicon detectors of the CHIMERA array

Mass and atomic-number identification (ID) of reaction products is a fundamental requirement of any nuclear reaction study. An effective particle-ID method is demonstrated, based on pulse shape analysis/discrimination (PSD) applied to large-area, single-element silicon detectors. This technique uses commercial electronic modules and achieves atomic number resolution rivaling that typically obtained with multi-element (/spl Delta/E-E) detector telescopes. The method is applied to the CHIMERA detector system without compromising its time-of-flight (TOF) resolution. In-beam tests of the PSD method have been performed with large-area, 300-/spl mu/m thick CHIMERA silicon detectors, measuring particles from the /sup 19/F+/sup 12/C reaction at Tandem energies. Performance of a simple PSD set up is discussed, for front and rear particle injection.

CHIMERA data acquisition via digital sampling technique

A 100 Msamples/s 14-bit sampling analog-to-digital converter has been used to perform digital pulse-shape acquisition of signals collected from CHIMERA telescopes. Two different kinds of tests have been carried out to check the performances. The signals from a typical CHIMERA detection cell have been collected using both a standard CHIMERA electronic chain up to the amplifier, and a very simple analog front end, basically reduced to the preamplifier. The obtained on-beam and on-line results are presented.

Charge identification in large area planar silicon detectors, using digital pulse shape acquisition

The capability of digital pulse shape technique to acquire data from CHIMERA detection cells (Si-CsI(Tl) telescopes) has been evidenced in our previous works. We have now applied this technique to the charge discrimination of the products stopped in the silicon detectors. Large area totally depleted CHIMERA planar silicon detectors (5 cmtimes5 cm area, 300 mum thick) in both rear and front side injection have been used. In preliminary tests full charge identification for the reaction products up to Z=11 have been obtained for products both crossing (DeltaE-E technique) and stopping in the silicon detector, using a 21 MeV/u 20Ne beam at the LNS Superconducting Cyclotron in Catania. The quality of the obtained results clearly indicates that the digital signal processing approach is able to give excellent results in this application, too

A low-noise charge amplifier with fast rise time and active discharge mechanism

A new hybrid, low-noise, wide-bandwidth charge amplifier, using a new active discharge mechanism, has been designed and built primarily for gamma-ray tracking detectors, where a fast rise time is required. In order to realize the discharge of the feedback capacitance, a noninverting low-gain (A) stage has been inserted between the output of a conventional charge preamplifier and the high-value feedback resistance. This technique allows to make the discharge time constant shorter (by factor A), while keeping the feedback resistor as the feedback capacitance unchanged. Special care has been devoted realizing the hybrid layout to reduce the stray capacitance of the feedback resistor and particular attention has been dedicated to assure a good signal-to-noise ratio and a fast rise time. A low-power consumption allows the use of this charge-sensitive preamplifier in vacuum chamber without cooling system. The noise level is equivalent to less than 880-eV full width half maximum for an input capacitance of 22 pF, using 3-/spl mu/s shaping time. The noise grows with a slope of less than 10 eV/pF in the range of 20-60 pF input capacitance. This suggests that the preamplifier can be operated at room temperature maintaining a good noise usually reachable with a cooled setup.

A 16-channel programmable antialiasing amplifier

We designed and built a 16-channel NIM module acting as preliminary analog processing of the signals to be converted by sampling ADCs for the CHIMERA 4π multidetector digital pulse shape acquisition system. The main functions of the module are: i) a second order anti-aliasing filter with two programmable cutting frequencies, ii) a programmablegain amplifier to cope with the full dynamic range of the ADC, iii) a programmable output offset voltage with AC or DC input coupling selection. In addition, a buffered replica of input signals is present on the front panel to serve the conventional analog acquisition chain. All the module parameters are programmable through an RS485 serial interface.

Digital Signal Processing for Mass Identification in a

CHIMERA is the only 4 pi-multidetector, used in intermediate nuclear physics experiments, able to perform mass identification of the reaction products. To this purpose, it employs time of flight measurements done with traditional time to digital converters. In order to improve the resolution in mass identification, we have applied digital signal processing to time of flight measurements. This paper presents the methodology for data analysis, the adopted algorithms and the results obtained at different sampling frequencies (mass identification up to A = 33 for the reaction products produced by a 20.5 MeV/u 20Ne beam on 27Al target).

4\pi

The capability of digital pulse shape technique to acquire data from CHIMERA detection cells (Si-CsI(Tl) telescopes) has been evidenced in our previous works. /spl Delta/E-E scatter plots to obtain charge identification for the detected reaction products and fast-slow scatter plots from the CsI(Tl) light pulses for light charged product identification have been carefully reconstructed. We have now applied this technique to the charge discrimination of the products which stop in the silicon detectors, by using large area totally depleted CHIMERA silicon detectors (300 /spl mu/m thick, 5/spl times/5 cm/sup 2/ area) in reverse mount. In preliminary tests full charge identification for the reaction products up to Z=11 have been obtained for products both crossing the silicon detector (/spl Delta/E-E technique) and stopping in it, using a 21.1 MeV/u /sup 20/Ne beam at the LNS superconducting cyclotron in Catania. The quality of the obtained results clearly indicates that the digital signal processing approach is able to give excellent results in this application, too.

-Detector, Using Time of Flight Measurement

The Farcos project (Femtoscope Array for Correlations and Spectroscopy) is discussed in this contribution. It consists of a new detector array designed and constructed by Exochim-Chimera group at INFN of Catania and Laboratori Nazionali del Sud. The array is described in its design and scientific goals to address. Some of the first preliminary tests with radioactive sources and beams are also discussed, together with some highlights of future perspectives.