Proton and α sequential emission in the 16 O + 58 Ni deep inelastic reaction: a semi classical approach

Full text: In the framework of heavy-ion reactions, at incident energies available at tandem accelerators, for projectile-target systems showing a weak binary fission probability, emission of energetic particles and light clusters from the continuous part of the spectra of the ejectiles has been discovered, stimulating the development of many theoretical models and approaches. After a peripheral collision, two fragments with masses and charges close to projectile and target are produced, together with a few light particles, and the observed energy and angular correlations between these particles and the reaction fragments have been described by means of a sequential emission from the detected projectile- like and the undetected target-like fragments. The experimental spectra clearly show that a significant fraction of the yield of the highly energetic light particles is emitted in the forward region, showing a doubly forward-peaked structure, not explainable in terms of a statistical emission from the accelerated fragments, revealing the presence of an important non-equilibrium component in the particle emission. A theoretical approach has been developed to describe the non-equilibrium and the evaporative components of the sequential particle emission in peripheral heavy ion collisions. By studying the non-equilibrium sequential component of the particle emission it is possible to probe the early stage of the collision, obtaining reaction mechanism information complementary to what one usually extracts from the two-body reactions angular distributions. We applied this approach to the angular distributions of protons and -particles emitted in coincidence with projectile-like fragments in the deep inelastic collision 58 Ni(16 O, (C, N, O))(Zn, Cu, Ni) performed at 132 MeV laboratory energy at IReS, Strasbourg. We defined a positive alignment parameter on a quantization axis perpendicular to the reaction plane, related to the polarization effects induced on the decaying target-like nucleus during the first step of the reaction. In our application this parameter assumes the values 0.80, 0.77 and 0.74 for the -emission and 0.78, 0.88 and 0.86 for the emission, for Zn, Cu and Ni respectively. This result can be explained by assuming that, during the deep inelastic collision 16 O + 58 Ni at E160 = 132 MeV, only one type of semi-classical trajectory predominantly contributes. (Author)