F. Amorini

A monolithic silicon detector telescope

Abstract An ultrathin silicon detector (1 μm) thick implanted on a standard 400 μm Si-detector has been built to realize a monolithic telescope detector for simultaneous charge and energy determination of charged particles. The performances of the telescope have been tested using standard alpha sources and fragments emitted in nuclear reactions with different projectile-target colliding systems. An excellent charge resolution has been obtained for low energy (less than 5 MeV) light nuclei. A multi-array lay-out of such detectors is under construction to charge identify the particles emitted in reactions induced by low energy radioactive beams.

Evidence for α-particle condensation in nuclei from the Hoyle state deexcitation

Abstract The fragmentation of quasi-projectiles from the nuclear reaction 40Ca + 12C at 25 MeV/nucleon was used to produce excited states candidates to α-particle condensation. Complete kinematic characterization of individual decay events, made possible by a high-granularity 4π charged particle multi-detector, reveals that 7.5 ± 4.0 % of the particle decays of the Hoyle state correspond to direct decays in three equal-energy α-particles.

Isospin diffusion and equilibration for Sn+Sn collisions at E/A=35 MeV

Equilibration and equilibration rates have been measured by colliding Sn nuclei with different isospin asymmetries at beam energies of E/A=35 MeV. Using the yields of mirror nuclei of {sup 7}Li and {sup 7}Be, we have studied the diffusion of isospin asymmetry by combining data from asymmetric {sup 112}Sn+{sup 124}Sn and {sup 124}Sn+{sup 112}Sn collisions with those from symmetric {sup 112}Sn+{sup 112}Sn and {sup 124}Sn+{sup 124}Sn collisions. We use these measurements to probe isospin equilibration in central collisions where nucleon-nucleon collisions are strongly blocked by the Pauli exclusion principle. The results are consistent with transport theoretical calculations that predict a degree of transparency in these collisions, but inconsistent with the emission of intermediate mass fragments by a single chemically equilibrated source. Comparisons with quantum molecular dynamics calculations are consistent with results obtained at higher incident energies that provide constraints on the density dependence of the symmetry energy.

Results of the ASY-EOS experiment at GSI : the symmetry energy at suprasaturation density

Directed and elliptic flows of neutrons and light charged particles were measured for the reaction 197Au+197Au at 400 MeV/nucleon incident energy within the ASY-EOS experimental campaign at the GSI laboratory. The detection system consisted of the Large Area Neutron Detector LAND, combined with parts of the CHIMERA multidetector, of the ALADIN Time-of-flight Wall, and of the Washington-University Microball detector. The latter three arrays were used for the event characterization and reaction-plane reconstruction. In addition, an array of triple telescopes, KRATTA, was used for complementary measurements of the isotopic composition and flows of light charged particles. From the comparison of the elliptic flow ratio of neutrons with respect to charged particles with UrQMD predictions, a value \gamma = 0.72 \pm 0.19 is obtained for the power-law coefficient describing the density dependence of the potential part in the parametrization of the symmetry energy. It represents a new and more stringent constraint for the regime of supra-saturation density and confirms, with a considerably smaller uncertainty, the moderately soft to linear density dependence deduced from the earlier FOPI-LAND data. The densities probed are shown to reach beyond twice saturation.

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.

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

Pulse shape discrimination of charged particles with a silicon strip detector

Abstract A simple and effective pulse shape discrimination technique is applied to a silicon strip detector array. Excellent charge identification from H up to the Ni projectile has been obtained and isotope separation up to N has also been observed. The method we systematically studied is essentially based on a suitable setting of the constant fraction discriminators, and its main advantage is that no additional electronic modules are needed compared to the ones used in the standard TOF technique.

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

Odd-even staggering effects on charge distributions are investigated for fragments produced in semiperipheral and central collisions of 112Sn+58Ni at 35 MeV/nucleon. For fragments with Z<16 one observes a clear overproduction of even charges, which decreases for heavier fragments. In peripheral collisions staggering effects persist up to Z about 40. For light fragments, staggering appears to be substantially independent of the centrality of the collisions, suggesting that it is mainly related to the last few steps in the decay of hot nuclei.

-Detector, Using Time of Flight Measurement

The digital pulse shape data acquisition (DAQ) system used by the large area telescopes of the 4pi-multidetector CHIMERA requires transferring large amount of data to the computer. This is necessary so that the same information can be extracted from the detector pulses as in previous analog based systems. To overcome this problem, we have used a sampling ADC-board equipped with two TigerSHARC digital signal processors. The board receives the data and reconstructs the event parameters online. The data volume is significantly reduced by transmitting to the DAQ only the reconstructed event parameters