S.E.A. Orrigo

Core excited Fano-resonances in exotic nuclei

Abstract Fano-resonances are investigated as a new continuum excitation mode in exotic nuclei. By theoretical model calculations we show that the coupling of a single particle elastic channel to closed core-excited channels leads to sharp resonances in the low-energy continuum. A signature for such bound states embedded in the continuum (BSEC) are characteristic interference effects leading to asymmetric line shapes. Following the quasiparticle-core coupling model we consider the coupling of 1-QP (one-quasiparticle) and 3-QP components and find a number of long-living resonance structures close to the particle threshold. Results for 15 C are compared with experimental data, showing that the experimentally observed spectral distribution and the interference pattern are in qualitative agreement with a BSEC interpretation.

A low-pressure gas detector for heavy-ion tracking and particle identification

A low-pressure gas tracker for heavy ions is described. It is based on a drift chamber with four series of multiplying wires for energy loss measurement and underlying strips for position and angle determination. Results of tests with an α-source and with low-energy heavy-ion beams are presented. They indicate the suitability of such a detector in a wide range of experiments with heavy ions where a low energy threshold, a large solid angle, together with a precise measurement of ion trajectories and identification is needed. In particular, the application as a prototype of the focal plane detector for the large-acceptance spectrometer MAGNEX is discussed.

New lines of research with the MAGNEX large‐acceptance spectrometer

A new design of magnetic spectrometer, MAGNEX, is under construction for the INFN‐LNS, Catania. It is primarily intended for use with the Tandem‐accelerated radioactive beams from the EXCYT facility. Both projects are expected to be completed by early 2004. Considering the broad choice of both stable and radioactive beams that will be available at the LNS, the spectrometer provides new opportunities for, e.g., spectroscopy of weakly bound nuclei by direct reactions, reaction mechanisms with large isospin and nuclear astrophysics.

First Results from The MAGNEX Large Acceptance Spectrometer

The MAGNEX large‐acceptance spectrometer was commissioned with beams from the LNS Tandem. First results of physical interest are presented. The obtained 10−3 energy resolution confirms the ambitious characteristic of the calculations and allows considering the instrument as an ideal tool for future studies in the field of nuclear spectroscopy and reaction mechanisms at incident energies not far form the Coulomb barrier.

Exploring Light Neutron Rich Nuclei via the (7Li,7Be) Reaction

A systematic study of the nuclei that can be described as an integer number of α particles plus three neutrons via the (7Li,7Be) reaction at about 8 MeV/u has shown the presence of Bound States Embedded in the Continuum in the energy spectra. These are experimental signatures of the dynamical correlations of an easily polarizable core with a single‐particle state of the valence neutron.

First results and planned experiments with the INFN‐LNS ray‐tracing magnetic spectrometer MAGNEX

The MAGNEX large‐acceptance ray‐tracing magnetic spectrometer has recently been used with beams from the INFN‐LNS Tandem accelerator. After an accurate commissioning, the instrument has started an ambitious experimental program. In the first experiment the 19F(7Li,7Be)19O charge‐exchange reaction was studied at 52 MeV incident energy. The 19O excitation energy spectrum was reconstructed and the angular distributions measured. The second experiment was aimed at the study of the 15C via the 13C(18O,16O)15C reaction at 84 MeV incident energy. The ejectiles where detected at forward angles and mass identified by means of an innovative technique. The 15C excitation energy spectra up to about 20 MeV were obtained with a 250 keV FWHM energy resolution. In addition to several known states, the spectra show two unknown resonant‐like structures at 11.4 and 14.0 MeV. The strong population of these structures, together with the measured widths, could indicate the collective nature of these states associated to a corr...