M. Alderighi

Particle identification method in the CsI(Tl) scintillator used for the CHIMERA 4π detector

Abstract The charged particle identification obtained by the analysis of signals coming from the CsI(Tl) detectors of the CHIMERA 4 π heavy-ion detector is presented. A simple double-gate integration method, with the use of the cyclotron radiofrequency as reference time, results in low thresholds for isotopic particle identification. The dependence of the identification quality on the gate generation timing is discussed. Isotopic identification of light ions up to Beryllium is clearly seen. For the first time also the identification of Z =5 particles is observed. The identification of neutrons interacting with CsI(Tl) by ( n , α ) and ( n , γ ) reactions is also discussed.

Mass and charge identification of fragments detected with the Chimera Silicon-CsI(Tl) telescopes

Abstract Mass and charge identification of charged products detected with Silicon–CsI(Tl) telescopes of the Chimera apparatus are presented. An identification function, based on the Bethe–Bloch formula, is used to fit empirical correlations between Δ E and E ADC readings, in order to determine, event by event, the atomic and mass numbers of the detected charged reaction products prior to energy calibration.

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

Isotope correlations as a probe for freeze-out characterization: central124Sn+64Ni,112Sn+58Ni collisions

Abstract 124 Sn+ 64 Ni and 112 Sn+ 58 Ni reactions at 35 AMeV incident energy were studied with the forward part of CHIMERA multi-detector. The most central collisions were selected by means of a multidimensional analysis. The characteristics of the source formed in the central collisions, as size, temperature and volume, were inspected. The measured isotopes of light fragments (3 ⩽ Z ⩽ 8) were used to examine isotope yield ratios that provide information on the free neutron to proton densities.

Digital pulse shape technique for charge discrimination in reversed CHIMERA silicon detectors

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.

A spatial density analysis technique for the automatic classification of 4/spl pi/ detector data

In nuclear physics at intermediate energies, the use of multidetector arrays consisting of thousands of detectors is customary. This paper presents a novel approach to the automatic classification of data collected by the 4/spl pi/ detector CHIMERA, constituted by 1192 telescopes of a thin silicon transparent detector coupled to a thick CsI(Tl) scintillator. The method is based on spatial density data processing and produces frequency distributions of the most significant physical parameters. These one-dimensional spectra can be more easily analyzed than the standard two-dimensional scatter plots. With respect to manual or semiautomatic procedures, presently used for data analysis, our method offers the advantages of drastic time reduction and unbiased criteria for cluster identification. The proposed method can be successfully used in both off-line data analysis and multidetector stability control.

The enhanced data acquisition system for the 4/spl pi/ detector CHIMERA

CHIMERA is a second generation 4/spl pi/ detector for high resolution light particles and fragments measurements in the field of intermediate energy nuclear physics. An enhanced data acquisition, control and trigger system has been developed to manage the almost 5000 electronic channels of the detector. Data acquisition is based on fast data link (FDL) connection between 9U VME crates. FDL is a highly programmable VME device. It performs data readout and transfer to a destination board VME CPU, FIC8243, running the real time OS9 operating system. Data read and transfer is performed by a fast protocol (sparse data scan) whose performances have been improved introducing the chained block transfer mode (CELT) technique. Data collected by the CPU are broadcasted to the analysis stations for on-line data analysis and storage. All commands from and to VME CPU are sent by socket based network protocols. Complete remote control of the electronic front-end is obtained by a system of client-server applications. A first level event selection and control during readout is assured by a trigger system based on a new VME 9U board (MUSE), fully integrated with the FDL readout system.

The on-line computational and control system for the 4/spl pi/-detector CHIMERA

A commercial two-DSP-based board is the basic unit of the on-line computational and control system under development for the multidetector CHIMERA. The system design includes a small scale parallel and distributed architecture of PCs, used as both host and user and network interface, and of DSP boards, up to three for each host. The system is able to accomplish the on-beam control of CHIMERA, by means of the on-line computation of special algorithms, instead of using the usual techniques of special pulses to be sent off-beam. The physical data, collected and organized in UDP-packets by the data acquisition system, are read through a 10 Mbit/s Ethernet network. The PC-software, running under Windows NT 4.0, is based on threads and assures the communication and program managing and the result presentation. The DSP-software written in C++ takes care of the communication with the PC and of the computation. The preliminary on beam results for the first three wheels (about 100 telescopes), obtained employing two bi-processor boards located in the PCI-bus of a Pentium MMX PC are also presented.