E. Migneco

Measurements of light transmission in deep sea with the AC9 trasmissometer

The NEMO Collaboration aims to construct an underwater Cherenkov detector in the Mediterranean Sea, able to act as a neutrino telescope. One of the main tasks of this project, which implies difficult technological challenges, is the selection of an adequate marine site. In this framework the knowledge of light transmission properties in deep seawater is extremely important. The collaboration has measured optical properties in several marine sites near the Italian coasts, at depths > 3000 m; using a setup based on a AC9, a commercial trasmissometer, manufactured by WETLabs. The results obtained for the two sites reported in this paper (Alicudi and Ustica), show that deep seawater optical properties are comparable to those of the clearest waters. r 2002 Elsevier Science B.V. All rights reserved.

BaF2 scintillator: A stand-alone detector for γ-rays and light charged particles

Abstract The performances of thick (≥ 10 cm) BaF 2 crystals as detectors for γ-rays and light charged particles have been tested. The capability of BaF 2 of identifying Z = 1 particles by itself alone is shown. A new method to perform γ-particle and particle mass discrimination to be used in multiple coincidence experiments with highly segmented detection system is presented.

Strong impact parameter dependence of hard photon production in intermediate energy heavy ion collisions

Abstract The dependence of the high energy photon production on the impact parameter has been investigated in the reaction 129 Xe+ 197 Au at 44 MeV/u using the multidetector array MEDEA. A strong dependence of the high energy photon production probability on the impact parameter has been observed, while the slope parameter of the photon spectrum is almost constant. The data support the interpretation of the hard photon production in terms of first chance n-p collisions.

On the origin of fast proton emission in intermediate energy heavy ion collisions

Abstract Exclusive measurements of multiplicity distributions of fast protons emitted in 40Ar and 132Xe induced reactions at 44 MeV/u bombarding energy have been performed using MEDEA 4π detection sytem. The data reflect the impact parameter dependence of the overlap region size and scale from system to system as the number of participant protons. The hypothesis of pre-equilibrium emission following first order p-N collisions is consistent with the data.

Response of the BaF2 scintillator to light charged particles

The response of a large BaF2 scintillator crystal in terms of analog output and energy resolution dependence on the light charged particles kinetic energy in the 4–150 MeV/u range has been investigated. The occurrence of loss mechanisms in the kinetic energy to light yield conversion is observed. A model calculation, based on the electron-hole recombination to trapping competition and the occurrence of ionization quenching, gives results in very good agreement with the experimental data. The detector energy resolution is found to be consistent with the photoelectron statistics as the main contribution. A procedure for reproducible particle energy calibration, based on the cosmic muon energy deposition in the BaF2 as reference is established.

Different isotopic composition as a signature for different processes leading to fragment production in midperipheral 58Ni+58Ni collisions at 30 MeV/nucleon

We report on the results of experiments performed to investigate the 58 Ni + 58 Ni 30 MeV/nucleon reaction. In midperipheral collisions a massive fragment (4 Z 12) production has been observed. The emission patterns exhibit features consistent with dynamical fragmentation of a neck zone between the interacting nuclei, while in addition and at the same time, the projectile-like and targetlike residues are subject to statistical decay. The nature of the fragments produced via the two different mechanisms differ both for what concerns charge distribution and isotopic composition. In particular, neutron rich fragments can be produced in dynamical processes, even if the starting nuclear matter presents a N/Z ratio close to the unity.  2001 Elsevier Science B.V. All rights reserved.

Towards a better understanding of deep subthreshold photofission of238U

Deep subthreshold photofission data of238U are analysed. Spectroscopic properties of highly deformed states from experiments in the literature are introduced into a model calculation based on the doorway state formalism which is extended to fission at energies as low as the isomeric level. It is shown that starting from the results of a detailed analysis of the photofission measurements near the top of the fission barrier it is possible to describe the process in the energy range covered by the intermediate well in the double-humped deformation potential. In particular, the so-called “shelf effect” in the low energy photofission is reproduced in terms of delayed isomeric fission through a few undamped vibrational states localised in the pairing gap region above the isomer.

Strong Enhancement of Extremely Energetic Proton Production in Central Heavy Ion Collisions at Intermediate Energy

The energetic proton emission has been investigated as a function of the reaction centrality for the system (58)Ni + (58)Ni at 30A MeV. Extremely energetic protons (E(NN)(p) > or = 130 MeV) were measured and their multiplicity is found to increase almost quadratically with the number of participant nucleons, thus indicating the onset of a mechanism beyond one- and two-body dynamics.

Impact parameter dependence of linear momentum transfer and the role of two-body dissipation mechanisms in heavy ion collisions around the Fermi energy

Abstract High energy γ -rays ( E γ >35 MeV) have been measured in coincidence with heavy residues emitted in reactions induced by a 37 MeV/u 36 Ar beam on a 98 Mo target. The γ -ray yield increases strongly with increasing linear momentum transfer indicating the importance of two-body collisions in the transfer mechanism. The high energy γ -ray multiplicity has been used to correlate the linear momentum transfer to the impact parameter. This correlation is compared to dynamical BNV simulations to show the essential role of two body nucleon-nucleon collisions at these bombarding energies.

MACISTE: the forward spectrometer for heavy ions at LNS-Catania

The compact heavy ion spectrometer MACISTE is going to be realized at the Laboratorio Nazionale del Sud-Catania (LNS). It should allow one to resolve the single mass unit up to A/spl ap/70 and the single charge up to Z/spl ap/45 when operating on ions around 50 MeV/amu. Coupling this device with other multidetectors already installed at LNS will give access to a large series of experiments concerning the projectile-like and the quasi-fusion physics at intermediate energy.