Fusion and deep inelastic collisions studied on the Ar + Au system

Abstract

We investigated the Ar + Au system at two different bombarding energies 201 and 248 MeV. The mass and the energy of the products have been measured at different angles. Mass distributions exhibits two components separated at the low bombarding energy and partly merging into each other at the high bombarding energy. One of them can be attributed to fission following complete fusion, the other one is centered around mass 40 and corresponds to deep inelastic products. These two different mechanisms correspond to different time scales. Angular distributionsd ² σ/dθdM are peaked a little bit forward the grazing angle for products close to the projectile and, when the mass transfer increases, becomes constant. For deep inelastic collisions the mass transfer occurs in the way predicted using potential energy considerations, but the small FWHM and the slight shift of the position of the maximum of these distributions indicates a short contact time. Due to the increase of the temperature, the FWHM of the mass distribution of deep inelastic products increases with the bombarding energy. The mean total kinetic energy studied as a function of the detection angle shows the influence of statistical fluctuations at backward angles. One also observes for this system that the relaxation time connected with the mass asymmetry degree of freedom is larger than the one associated to the energy damping. Complete fusion cross sections measurements were also done at 183, 189 and 195 MeV which allowed to draw the excitation function for this process. Calculations of the fusion cross section using the concept of critical distance are in agreement with the data.