A. Nannini

Calibrating the CsI(Tl) detectors of the GARFIELD apparatus

The energy and charge dependence of the light output of the CsI(Tl) detectors of the GARFIELD apparatus has been investigated for heavy ions with 5pZp16 in the energy range from 2.2 to 8:3 A MeV: The results have been compared to an analytical expression successfully used in previous calibration procedures at higher energies, and a rather good agreement was obtained between measured and calculated quantities. The resulting parameter set was successfully applied to another set of experimental data. The overall result demonstrates the validity of the above mentioned calibration procedure in a wide range of incident ion energies and masses. r 2002 Elsevier Science B.V. All rights reserved. PACS: 29.40.Mc

Front-end electronics for the FAZIA experiment

FAZIA is a multidetector specifically designed to optimize A and Z reaction product identification in heavy-ion collision experiments. This multidetector is modular and based on three-layer telescopes made of two silicon detectors followed by a thick (10 cm) CsI(Tl) scintillator read-out by a photodiode. Its electronics is fully digital. The goal to push at maximum identification capability while preserving excellent energy resolution, can be achieved by using pulse-shape analysis techniques and by making an intensive use of high-speed flash ADCs. This paper presents the front-end part of the electronics.

Transition probabilities in the X(5) candidate

To investigate the possible X(5) character of {sup 122}Ba, suggested by the ground-state band energy pattern, the lifetimes of the lowest yrast states of {sup 122}Ba have been measured, via the recoil distance Doppler-shift method. The relevant levels have been populated by using the {sup 108}Cd({sup 16}O,2n){sup 122}Ba and the {sup 112}Sn({sup 13}C,3n){sup 122}Ba reactions. The B(E2) values deduced in the present work are compared to the predictions of the X(5) model and to calculations performed in the framework of the IBA-1 and IBA-2 models.

^{122}

Abstract. Symmetry energy is a key quantity in the study of the equation of state of asymmetric nuclear matter. Heavy ion collisions at low and intermediate energies, performed at Laboratori Nazionali di Legnaro and Laboratori Nazionali del Sud, can be used to extract information on the symmetry energy coefficient Csym, which is currently poorly known but relevant both for astrophysics and for deeper knowledge of the structure of exotic nuclei.

Ba

The γ -decay of the GDR in the 132 Ce compound nuclei produced by the reaction 64 Ni+ 68 Zn at Ebeam = 300 MeV, 400 MeV, 500 MeV (E ∗ of 100 MeV, 150 MeV and 200 MeV) has been measured. We have detected heavy recoil nuclei, light charged particles and γ -rays. The data obtained with the symmetric reaction 64 Ni+ 68 Zn indicate emission from a fully equilibrated compound nucleus as deduced from the analysis of charged particle spectra. The GDR parameters are found to be consistent with the predictions of the thermal fluctuation model. (Some figures in this article are in colour only in the electronic version)

Isotope analysis in central heavy ion collisions at intermediate energies

Preliminary analysis of the Hoyle-Gamma experiment is presented, where simultaneous gamma-particles detection for the α + 12C → α + (12C* + γ) reaction is used to suppress the background various orders of magnitude. This will allow us to measure very small Γ partial widths of 12C. Details of the method, the implementation and CHIMERA software analysis are presented as well as preliminary results.

The γ-decay of the GDR in highly excited Ce nuclei

The 48 Ti on 40 Ca reactions have been studied at 300 and 600 MeV focusing on the fusion-evaporation (FE) and fusion-fission (FF) exit channels. Energy spectra and multiplicities of the emitted light charged particles have been compared to Monte Carlo simulations based on the statistical model. Indeed, in this mass region (A 100) models predict that shape transitions can occur at high spin values and relatively scarce data exist in the literature about coincidence mea- surements between evaporation residues and light charged particles. Signals of shape transitions can be found in the variations of the lineshape of high energy gamma rays emitted from the de-excitation of GDR states gated on di erent region of angular mo- menta. For this purpose it is important to keep under control the FE and FF processes, to regulate the statistical model parameters and to control the onset of possible pre- equilibrium emissions from 300 to 600 MeV bombarding energy.

First results of the Hoyle-Gamma experiment: study of the excited levels in carbon-12 gamma decay

The degree of isospin mixing in the hot compound nucleus 80Zr has been extracted by statistical-model analysis of the γ-decay spectrum emitted in fusion reactions 40Ca+40Ca at Ebeam = 200 MeV and 37Cl+44Ca at Ebeam = 153 MeV. In the case of 40Ca+40Ca reaction an hindrance of first-step γ-decay is expected because in self-conjugate nuclei the E1 selection rules forbid the decay between states with isospin I=0. The results obtained at finite temperature (T ~ 2 MeV) have been used to extrapolate the degree of mixing at zero temperature

Measurement of light charged particles in the decay channels of medium-mass excited compound nuclei

In heavy ion nuclear reactions the process leading to complete fusion is expected to produce pre-equilibrium γ-ray emission, if particular conditions are met. Indeed, when there is an N/Z asymmetry between projectile and target, charge equilibration takes place with a collective dipole oscillation, called Dynamical Dipole (DD), associated to a γ-ray emission. The existing experimental data concerning this pre-equilibrium γ-ray emission are still rather scarce and manly concentrated in the A≊132 mass region. The very preliminary results concerning the measurement of the DD γ-ray emission in the fusion reaction 16O (Elab=192 MeV) + 116Sn at 12 MeV/u will be presented and compared with the γ yield measured for the same reaction at 8.1 and 15.6 MeV/u. The present experiment aims at the measurement of the total emission yield of the DD at 12 MeV/u where the predicted theoretical yield does not completely reproduce the experimental data. The experiment has been performed at the INFN Legnaro Laboratories using the GARFIELD-HECTOR array.

Isospin mixing at finite temperature in80Zr

Isospin mixing induced by Coulomb interaction has been measured in the compound nucleus Z = N = 40 80Zr at T∼2 MeV produced in a fusion‐evaporation reaction. The observable sensitive to the isospin purity of the compound nucleus is the Giant Dipole Resonance γ decay. The degree of mixing of the compound nucleus has been obtained via Statistical Model analysis of the measured γ spectrum.