[en] In this paper, the use of a fast digitizing system for identification of fast charged particles with scintillation detectors is discussed. The three-layer phoswich detectors developed in the framework of the FIASCO experiment for the detection of light charged particles (LCP) and intermediate mass fragments (IMF) emitted in heavy-ion collisions at Fermi energies are briefly discussed. The standard analog electronics treatment of the signals for particle identification is illustrated. After a description of the digitizer designed to perform a fast digital sampling of the phoswich signals, the feasibility of particle identification on the sampled data is demonstrated. The results obtained with two different pulse shape discrimination analyses based on the digitally sampled data are compared with the standard analog signal treatment. The obtained results suggest, for the present application, the replacement of the analog methods with the digital sampling technique

[en] An application of digital sampling techniques is presented which can simplify experiments involving sub-nanosecond time-mark determinations and energy measurements with nuclear detectors, used for Pulse Shape Analysis and Time of Flight measurements in heavy ion experiments. The basic principles of the method are discussed as well as the main parameters that influence the accuracy of the measurements. The method allows to obtain both time and amplitude information with an electronic chain simply consisting of a charge preamplifier and a fast high resolution ADC (in the present application: 100 MSample/s, 12 bit) coupled to an efficient on-line software. In particular an accurate Time of Flight information can be obtained by mixing a beam related time signal with the output of the preamplifier. Examples of this technique applied to Silicon detectors in heavy-ions experiments involving particle identification via Pulse Shape analysis and Time of Flight measurements are presented. The system is suited for applications to large detector arrays and to different kinds of detectors

[en] An application of digital sampling techniques is presented which can greatly simplify experiments involving sub-nanosecond time-mark determinations and energy measurements with nuclear detectors, used for Pulse Shape Analysis and Time of Flight measurements in heavy ion experiments. In this work a 100 M Sample/s, 12 bit analog to digital converter has been used: examples of this technique applied to Silicon and CsI(Tl) detectors in heavy-ions experiments involving particle identification via Pulse Shape analysis and Time of Flight measurements are presented. The system is suited for applications to large detector arrays and to different kinds of detectors. Some preliminary results regarding the simulation of current signals in Silicon detectors are also discussed. (authors)

[en] It is well known that the resistivity non-uniformity of silicon detectors is a crucial parameter when pulse-shape analysis is used to identify the charge and the mass of stopped heavy ions. In this work a method is described that allows a direct absolute resistivity measurement of the detector as a function of the position (∼mm resolution). The detector is used in a reverse-mount configuration and signals are collected for various applied voltages and for various (x,y) positions by using a point excitation. For each applied voltage-position combination, the average signal risetime is obtained via a digital pulse-shape analysis, finally allowing the extraction of the desired resistivity measurement as a function of the position. The method is non-destructive and can be applied to detectors with arbitrary shapes and readout geometries. Detectors can be fully tested in the laboratory before the actual experiments, possibly rejecting before beam time those not satisfying the resistivity uniformity requirements of the experiment.

[en] The FIASCO multidetector is a low-threshold apparatus, optimized for the investigation of peripheral to semi-central collisions in heavy ion reactions at Fermi energies. It consists of three types of detectors. The first detector layer is a shell of 24 position-sensitive Parallel Plate Avalanche Detectors (PPADs), covering about 70% of the forward hemisphere, which measure the velocity vectors of the heavy (Z > or approx. 10) reaction products. Below and around the grazing angle, behind the most forward PPADs, there are 96 ΔE-E silicon telescopes (with thickness of 200 and 500 μm, respectively); they are mainly used to measure the energy of the projectile-like fragment and to identify its charge and, via the time-of-flight of the PPADs, also its mass. Finally, behind most of the PPADs there are 158 (or 182, depending on the configuration) scintillation detectors, mostly of the phoswich type, which cover 25-30% of the forward hemisphere; they identify both light charged particles (Z=1,2) and intermediate mass fragments (3≤Z < or approx. 20), measuring also their time-of-flight

[en] Peripheral and semiperipheral collisions have been studied in the system ⁹³Nb+⁹³Nb at 38A MeV. The evaporative and midvelocity components of the light charged particle and intermediate mass fragment emissions have been carefully disentangled. In this way it was possible to obtain the average amount not only of charge and mass, but also of energy, pertaining to the midvelocity emission, as a function of an impact parameter estimator. This emission has a very important role in the overall balance of the reaction, as it accounts for a large fraction of the emitted mass and for more than half of the dissipated energy. As such, it may give precious clues on the microscopic mechanism of energy transport from the interaction zone toward the target and projectile remnants

[en] A systematic investigation of the average multiplicities of light charged particles and intermediate mass fragments emitted in peripheral and semiperipheral collisions is presented as a function of the beam energy, violence of the collision, and mass of the system. The data have been collected with the FIASCO setup in the reactions ⁹³Nb+⁹³Nb at (17,23,30,38)A MeV and ¹¹⁶Sn+¹¹⁶Sn at (30,38)A MeV. The midvelocity emission has been separated from the emission of the projectile-like fragment. This last component appears to be compatible with an evaporation from an equilibrated source at normal density, as described by the statistical code GEMINI at the appropriate excitation energy. On the contrary, the midvelocity emission presents remarkable differences in both the dependence of the multiplicities on the energy deposited in the midvelocity region and the isotopic composition of the emitted light charged particles

[en] Evidence for the dependence of excitation energy sharing between two heavy remnants on the difference in the lost mass in two-body peripheral heavy ion reactions at Fermi energy is presented, based on experimental results for the reactions ⁹³Nb+¹¹⁶Sn, ¹¹⁶Sn+⁹³Nb, and ⁹³Nb+⁹³Nb at 38A MeV. An observable based on the experimental velocities of the heavy residues is used to select reactions with equal preevaporative masses of projectile-like fragments and target-like fragments. The excitation energy, evaluated by means of a complete average calorimetry, is found to be larger for the nucleus that finally retains a larger part of the hot interaction region

[en] Light charged particles emitted at about 90 deg. in the frame of the projectile-like fragment in semiperipheral collisions of ⁹³Nb+⁹³Nb at 38A MeV give evidence for the occurrence, in the same class of events, of two different production mechanisms. This is demonstrated by differences in the kinetic energy spectra and in the isotopic composition of the particles. The emission with a softer kinetic energy spectrum and a low N/Z ratio for the hydrogen isotopes is attributed to an evaporation process. The harder emission, with a much higher N/Z ratio, can be attributed to a midvelocity process consisting of a nonisotropic emission, on a short time-scale, from the projectile-like fragment

No abstract available