A. Brondi

Improvements in the in-beam γ-ray spectroscopy provided by an ancillary detector coupled to a Ge γ-spectrometer: the DIAMANT-EUROGAM II example

For the first time the 4π γ-ray spectrometer EUROGAM II has been coupled to a 4π light charged particle detector array, DIAMANT, during a test experiment on the reaction 32S + 58Ni at 120 MeV beam energy. A very large improvement in the peak-to-background ratio of the γ-spectra has been found when EUROGAM II is triggered by DIAMANT to select an exit channel. A simple algebra has been developed which provides theoretical estimates in good agreement with these experimental results. It is demonstrated that, depending on both the γ-spectrometer and ancillary detector performances, much better peak-to-background can be obtained by such a coupling. For the same peak-to-background ratio, the use of an ancillary detector allows for a lower γ-ray coincidence level and therefore improves the statistics. Ways to select the most appropriate ancillary detector are given. The ability of the ancillary detector to provide a total Doppler shift correction is crucial for the improvement of the peak-to-background ratio.

The 8/spl pi/LP project: A 4/spl pi/ light charged particle detection array at LNL

A 4/spl pi/ detection system sensitive to light charged particles is being developed at the Laboratori Nazionali di Legnaro (LNL) for the study of the reaction mechanisms produced in heavy ion collisions at energies up to 20 AMeV. The 8/spl pi/LP apparatus is a telescope assembly characterized by large solid angle (90% of 4/spl pi/) and high granularity (262 modules). Particle identification at low energy is obtained by combining /spl Delta/E-E, TOF and PSD techniques. Each telescope is made of a 300 /spl mu/m passivated silicon detector and a 15 mm (or 5 mm) CsI(Tl) crystal with photodiode readout. Thresholds for particle identification range from 1 MeV for protons and 3 MeV for alpha particles to about 2-3 AMeV for C ions. A low-cost trigger and readout bus system has been developed to cope with the large number of parameters and the high counting rate. The system will be fully operational for experiments in the summer of 1997.

The Italian AMS program: Measurements with the Naples TTT-3 tandem accelerator

Abstract The HVEC model TTT-3 tandem accelerator at the University of Naples has been modified for high energy mass spectrometry measurements. The new injector includes an ANIS sputter source and a 35° inflection magnet, both manufactured by Danfysik. A switching magnet was also added to the beam transport system and the final detector was mounted on the 30° beam line dedicated to AMS. Preliminary measurements and limits of the present system are discussed.

Pre-scission emission and evaporation residues survival probability in the reaction 37Cl + 120Sn at 187 MeV

Abstract Light particles spectra in coincidence with fission fragments have been measured for the reaction 187 MeV 37 Cl on 120 Sn populating 157 Ho compound nuclei at the excitation energy E x = 85 MeV. The experimental neutron pre-scission multiplicity for symmetric splintting is two times larger than the statistical model estimate. The experimental multiplicity is reproduced by calculations in which a fission delay, in agreement with systematics, is introduced. This empirical fission delay produces a sizeable increase, with respect to the standard statistical model estimate, of the survival probability against fission for nuclei with angular momentum around J ∼ h . The importance of this effect in the population of superdeformed and hyperdeformed structures in the evaporation residues is discussed.

Alpha particle emission, incomplete fusion and population of high-spin states in the reaction 120 MeV 19F + 181Ta

Abstract The reaction 120 MeV 19 F + 181 Ta has been studied by charged particle-γ-ray coincidence techniques. An incomplete fusion component has been identified in coincidence with 192,191 Hg residues which are populated in the αxn channels. Evidence has been found that the feeding of high spin states in final residues is enhanced when the coincidence is required with alpha particles emitted at forward angles, where the incomplete fusion component dominates.

AMS at the TTT-3 tandem accelerator in Naples

Abstract The Italian AMS facility, based on the TTT-3 tandem accelerator of the University of Naples, is now becoming operational for routine 14C measurements. The present configuration of the system and the first results obtained are discussed together with the improvements planned for the near future.

Proton direct capture on 40Ca

Abstract Excitation functions for the 40Ca(p, γ)41Sc reaction have been measured at 0° and 90° in the proton energy range Ep = 2.1–3.1 MeV. The experimental results have been interpreted in terms of the direct capture process to the first excited state of 41Sc. The direct capture transition to the ground state has been observed only at a few proton energies. The spectroscopic factor of the first excited state in 41Sc has been found to be 1.0 ± 0.3. The direct capture cross section to the ground state is consistent with the spectroscopic factor reported from stripping reactions.

Proton spectra in coincidence with super- and hyper-deformed structures in 152Dy

Abstract The hyperdeformed ridge structure recently observed in the reaction of 187 MeV 37 Cl on 120 Sn has been confirmed in a new proton-γ coincidence experiment at the GASP spectrometer and assigned to the nucleus 152 Dy. Proton spectra have been measured in coincidence with γ-rays belongings to the different structures in 152 Dy (oblate, prolate, super- and hyper-deformed). The deformation of the final evaporation residue affects only weakly the proton evaporation from the compound nucleus. Evidence has been found that the energy of the protons in coincidence with the hyperdeformed structure is larger than expected. This effect is discussed in the framework of the fission-evaporation competition.

Fission dynamics with the 4π detector 8πLP

A 4π light charged particle spectrometer, named 8πLP, is in operation at the Laboratori Nazionali di Legnaro (Italy) for the study of the reaction mechanisms produced in low-energy heavy-ion reactions. The spectrometer has recently been used in a study of fission dynamics that involves the detection of light charged particles in the fission and evaporation residue channel in a system of intermediate fissility, as well as in a study of multinucleon transfer to heavy target. Data on the system 240 MeV 32S + 100Mo are presented. Dynamical effects extracted as a consequence of the comparison of the data to the statistical model calculations are discussed.

The 8πLP project at LNL: a 4π light charged particle detection system

Abstract A new experimental set-up is under development at LNL to detect light charged particles with high efficiency and low thresholds. This apparatus is devoted to reaction mechanism studies and it is scheduled to be ready in 1997.