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Evaporative proton and alpha particle energy spectra and angular distributions have been measured in the decay of the compound nucleus 139Eu produced at an excitation energy of 90 MeV by the 32S + 107Ag reaction. In-plane and out-of-plane angular distributions and energy spectra of alpha particles have been compared with theoretical calculations performed using the statistical Montecarlo code Lilita. Three expressions for the level density parameter have been used: a) without isospin dependence b) with N-Z isospin dependence and c) with Z-Z0 isospin dependence, based on the distance of the nucleus from the valley of stability. The predictions by the Z-Z0 prescription fail to reproduce the data. Isospin independent and N-Z dependence reasonably well reproduce the data.

MeV/nucleon, with the aim to probe its evolution with incident energy. These reactions populate, through entrance channels having different charge asymmetries, the 132 Ce compound nucleus at an excitation energy of 117 MeV with identical spin distribution. Fusion events were selected by detecting high-energy γ-rays in coincidence with evaporation residues. The present results can be compared directly with those related to the same reactions at Elab � 9 MeV/nucleon where the compound nucleus excitation energy was equal to 173.5 MeV [1]. This study could be of aid in the formation of superheavy elements. In fact, the emission of pre-equilibrium dipole photons could represent an efficient new cooling mechanism of the composite system in charge asymmetric ”hot” fusion reactions, increasing thus its survival probability against fission [2]. EXPERIMENTAL SET-UP The experiment was performed by using the pulsed beams of 32 S and 36 S provided by the heavy-ion 15 MV Tandem-XTU accelerator of the Laboratori Nazionali di Legnaro (Italy) at Elab = 196 MeV and 214.2 MeV, respectively, impinging on 550 � g/cm 2 thick 100 Mo ( 97.42%) and 96 Mo ( 95.9%) self-supporting targets. The beam consisted of � 2 ns wide bunches with a 400 ns separation and it was measured in a Faraday cup shielded with lead and paraffin to reduce the background due to γ-rays and neutrons. Beam current was about 10 nA. The γ-rays were detected by using six seven-pack clusters of BaF2 scintillators situated at 28 cm from the target at different θ angles with respect to the beam direction. The total solid angle covered by all the clusters was 1.6 sr. Each cluster was surrounded by a 3 mm thick lead shield which reduced the counting rate due to the low energy γ-rays to 50% and stopped the charged particles. The evaporation residues were detected by means of four position sensitive Parallel Plate Avalanche Counters (PPAC’s) located at θ = 7 ◦ symmetrically around the beam direction at 70 cm from the target. The total solid angle covered by the PPAC’s was 0.089 sr. They provided the time of flight (TOF) with respect to the radiofrequency signal of the accelerator, the energy loss (�E) and the position of the reaction products. The energy calibration of the γ-ray detectors was obtained by using the sources 60 Co, 88 Y, the composite source of 241 Am+ 9 Be and the 15.1 MeV γ-rays from the p+ 12 C reaction. Down-scaled single events together with coincidence events between a PPAC and at least one fired BaF2 scintillator were collected during the experiment. A coincidence event was accepted if the deposited energy in a BaF2 cluster was greater than � 5 MeV. The threshold of each BaF2 scintillator was set at � 100 keV. The coincidence request eliminated any cosmic ray contamination of the γ-ray spectra.

We have started a research program at LNL with the apparatus 8πLP aimed at studying the fission dynamics in systems of intermediate fissility using light charged particles as probes. These systems are characterized by an evaporation residues (ER) cross section comparable or larger than the fission cross section, and by a relatively higher probability for charged particle emission in the pre-scission channel. In a theoretical framework in which time scale estimates rely on statistical model calculations, the additional analysis of particle emission in the ER channel allows to put more constraints on the input parameters of statistical and dynamical models. The presentation will report about an overall view of the systems studied so far and will provide clues for interesting physical cases. Recent advancement will also be discussed on the interplay between the fission and the evaporation residues channels as implied by a dynamical approach to the description of the fission process.

Light charged particles in coincidence with evaporation residues and heavy fragments have been measured for the 200MeV S-32 + Mo-100 reaction leading to the Ce-132 composite. The alpha pre-scission multiplicities are remarkably larger than what found in the same system at 240 MeV. This unexpected trend can be ascribed to the opening of the fast fission channel at 240 MeV. The statistical model reproduces the light charged particles pre-scission multiplicities at 200 MeV if a delay time of tau(d) approximate to 26 x 10(-21)s is considered.

The S-32 + Mo-100 and S-36 + Mo-96 fusionlike reactions were studied at incident energy of E-lab = 298 MeV and 320 MeV, respectively, with the aim of probing the influence of the entrance channel charge asymmetry on the dipole gamma-ray emission. The excitation energy and spin distribution of the compound nucleus created in these reactions were identical, the only difference being associated with the unequal charge asymmetry of the two entrance channels. High-energy gamma-rays were detected in an array of 9 seven-pack BaF2 clusters. Coincidence with fusionlike residues detected in four PPAC ensured the selection of central reaction events. By studying the differential gamma-ray multiplicity associated with the two reactions it was shown that the dipole strength excited in the compound nucleus increases with the entrance channel charge asymmetry. From the linearized spectra, the increase of the GDR gamma-ray intensity was found to be similar to25% for the more charge asymmetric system. The results are discussed and compared with those of previous data obtained at different incident energies.