F. Gramegna

Statistical Multifragmentation in Central Au+Au Collisions at 35 MeV/u

Abstract Multifragment disintegrations, measured for central Au + Au collisions at E A = 35 MeV , are analyzed with the Statistical Multifragmentation Model. Charge distributions, mean fragment energies, and two-fragment correlation functions are well reproduced by the statistical breakup of a large, diluted and thermalized system slightly above the multifragmentation threshold.

Optical and Scintillation Properties of Polydimethyl-Diphenylsiloxane Based Organic Scintillators

Polysiloxane based scintillators with high light yield have been synthesized. The polymer consists in cross-linked polydimethyl-co-diphenylsiloxane with different molar percentages of phenyl units. 2,5-diphenyl oxazole (PPO) and 2,5-bis(5-ter-butyl-2-benzoxazolyl)thiophene (BBOT) have been dispersed in the polymer as dopants. The energy transfer and scintillation capabilities have been investigated, for two different amounts of phenyl groups in the polymer network and for different concentrations of dye molecules, by means of fluorescence spectroscopy, ion beam induced luminescence (IBIL) and scintillation yield measurements with ¿ particles from an 241Am source. The luminescence features and the scintillation yields have been correlated to the composition of the scintillators.

Position sensitive and Bragg curve spectroscopy detector system

Abstract A heavy ion gas detector system consisting of a Bragg-curve spectroscopy ionization chamber for particle identification and a multiwire proportional chamber as position sensitive fast trigger device is described. The Bragg IC has been tested with several beams up to Z = 36 to investigate some aspects of the BCS method. Results are reported on energy resolution and linearity, Z resolving power and mass sensitivity. The energy resolution is well below 1%. The Bragg-peak amplitude is fairly independent of the energy in a wide energy range and single elements are identified up to Z = 38 with a resolving power Z / ΔZ − 50-80. Isotope identification by range measurement is limited by the straggling in the ionization process and the mass resolving power is M / ΔM ∼ 20–26 for S and Si isotopes. The MWPC allows subnanosecond time resolution and position identification along the in-plane coordinate within ±0.5 mm.

Multifragment production in Au+Au at 35 MeV/u

Abstract Multifragment disintegration has been measured with a high efficiency detection system for the reaction Au + Au at E / A = 35 MeV. From the event shape analysis and the comparison with the predictions of a many-body trajectories calculation the data, for central collisions, are compatible with a fast emission from a unique fragment source.

Circumstantial evidence for critical behavior in peripheral Au+Au collisions at 35 MeV/nucleon.

The fragmentation resulting from peripheral Au + Au collisions at an incident energy of {ital E}=35 MeV/nucleon is investigated. A power-law charge distribution, {ital A}{sup {minus}{tau}} with {tau}{approx_equal}2.2, and an intermittency signal are observed for events selected in the region of the Campi scatter plot where {open_quote}{open_quote}critical{close_quote}{close_quote} behavior is expected. {copyright} {ital 1996 The American Physical Society.}

The SPES Project at LNL

The main goal of the SPES project at Laboratori Nazionali di Legnaro of INFN (Italy) is to provide an accelerator system to perform forefront research in nuclear physics by studying nuclei far from stability. The SPES project is based on the production of neutron‐rich radioactive nuclei in the mass range 80 to 160, by the fission of uranium at the rate of 1013 fission/s. The Radioactive Ion Beam (RIB) will be produced by the Isotope Separator On Line (ISOL) technique using the proton‐induced fission in a uranium carbide target. The energy of the radioactive beams on target will range from a few MeV/u up to 10 MeV/u for A = 130 using the existing ALPI linac as the post‐accelerator.

Test of dynamical effects in the decay of the 59Cu compound nucleus

Abstract The energy spectra of α particles emitted in multiple-α decay chains from 59Cu compound nuclei formed in the reaction of 190 MeV 32S on 27Al have been measured. These spectra are sensitive to different regions of the phase space open to the decay of the compound nucleus. A direct test of dynamical effects related to the shape relaxation is obtained by comparing the experimental spectra with results from Monte Carlo statistical model calculations.

Hybrid detectors for neutrons combining phenyl-polysiloxanes with 3D silicon detectors

We report on the initial results of a research project aimed at the development hybrid detectors for fast neutrons by combining a phenyl-polysiloxane-based converter with a 3D silicon detector. To this purpose, new 3D sensor structures have been designed, fabricated and electrically tested, showing low depletion voltage and good leakage current. Moreover, the radiation detection capability of 3D sensors was tested by measuring the signals recorded from alpha particles, gamma rays, and pulsed lasers. The converter has been poured into the 3D cavities with excellent coupling, as confirmed by cross-section SEM analyses. Preliminary tests with neutrons have been carried out on the first hybrid detector prototypes at the CN accelerator of INFN LNL. The device design and technology are discussed, along with the first results from the electrical and functional characterization.

Red emitting phenyl-polysiloxane based scintillators for neutron detection

In this work, the performances of new red emitting phenyl- substituted polysiloxane based scintillators are described. Three dyes were dispersed in a phenyl-polysiloxane matrix in order to shift the scintillation wavelength towards the red part of the visible spectrum. PPO, Lumogen Violet (BASF) and Lumogen Red (BASF) were mixed to the starting resins with different wt. % and the analysis of the different samples was performed by means of fluorescence measurements. The scintillation yield to alpha particles at the different dye ratios was monitored by detecting either the full spectrum or the red part of the emitted light. Finally, thin red scintillators with selected compositions were coupled to Avalanche Photodiode sensors, which are usually characterized by higher efficiency in the red part of the spectrum. An increased light output of about 17% has been obtained comparing the red scintillators to standard blue emitting systems. Preliminary results on the detection of fast neutrons with the APD-red scintillator system are also presented.

The SPES project: An ISOL facility for exotic beams

SPES (Selective Production of Exotic Species) is an INFN project to develop a Radioactive Ion Beam (RIB) facility as an intermediate step toward EURISOL. The SPES project is part of the INFN Road Map for the Nuclear Physics development in Italy and is supported by the whole Italian Nuclear Physics community and mainly by LNL and LNS the INFN National Laboratories of Nuclear Physics in Legnaro and Catania. The Laboratori Nazionali di Legnaro (LNL) was chosen as the site for the facility construction due to the presence of the PIAVE-ALPI accelerator complex, which will be used as re-accelerator for the RIBs. The SPES project is based on the ISOL method with an UCx Direct Target and makes use of a proton driver of at least 40 MeV energy and 200 microA current. Neutron-rich radioactive beams will be produced by Uranium fission at an expected fission rate in the target in the order of 1013 fissions per second. The key feature of SPES is to provide high intensity and high-quality beams of neutron rich nuclei to perform forefront research in nuclear structure, reaction dynamics and interdisciplinary fields like medical, biological and material sciences. The exotic isotopes will be re-accelerated by the ALPI superconducting linac at energies up to 10AMeV for masses in the region of A=130 amu with an expected rate on target of 109 pps.