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CHIMERA is a 4π multidetector for charged particles available at Laboratori Nazionali del Sud (INFN‐LNS). A new method to measure the time scale of the emission of nuclear fragments is described, together with some applications in the field of the isospin dynamics of heavy‐ion collisions. Competition between fusion‐like and binary reactions near the energy threshold for nuclear multifragmentation is discussed. Opportunities are pointed out to use the detector at low and intermediate energies using the kinematical‐coincidence method.

The de-excitation of medium mass nuclei 118,134Ba produced in fusion process of 78,86Kr on 40,48Ca targets at 10 AMeV is studied, in order to investigate the isospin dependence of the decay modes; the neutron enrichment of the compound nuclei is in fact expected to play an important role on the emission mechanisms, providing crucial information on fundamental nuclear quantities such as level density, fission barrier, viscosity and symmetry energy. The experiment was performed at INFN-LNS with the 4π multidetector for charged particles CHIMERA, used for the first time in this low energy regime, thanks to a suitable Pulse Shape Discrimination method for charge identification applied to the silicon detectors. Preliminary results show a different isotopic composition and relative enrichment for the same Z in the two systems. The yields of the Intermediate Mass Fragments (IMF, 3

We investigated the prompt dipole γ‐ray emission, related with entrance channel charge asymmetry effects, in the 40Ar + 92Zr and 36Ar + 96Zr fusion reactions at Elab= 15 and 16 MeV/nucleon, respectively, with the aim to probe its evolution with incident energy. These reactions populate, through entrance channels having different charge asymmetries, the 132Ce compound nucleus at an average excitation energy of 304 MeV with identical spin distribution. Fusionlike events were selected by detecting high‐energy γ‐rays in coincidence with evaporation residues. By studying the differential γ‐ray multiplicity spectra of the considered reactions, it was shown that the dipole γ‐ray intensity increases by ∼14% for the more charge asymmetric system. This result, associated with those reported for the 32,36S + 100,96Mo reaction pair at lower beam energies, implies a “rise and fall” trend of the prompt dipole γ‐ray emission in the studied beam energy range with a maximum value at 9 MeV/nucleon.

The installation of CHIMERA multidetector, designed in order to study central collisions in heavy ion reactions at intermediate energy, is going on at LNS and the first experiment with the forward part (688 telescopes) is running since May 1999. The aim of this contribution is to present the status of the project.

Velocity distribution of mass identified evaporation residues produced in the {sup 32}S+{sup 12}C reaction at E({sup 32}S)=20 MeV/A have been measured using time-of-flight techniques. These distributions were used to separate the complete and incomplete fusion components. The complete fusion cross section and the deduced critical angular momenta are compared with other experimental data and the predictions of existing models.