Publication

Abstract : We have successfully carried out an optical model analysis of 16O + 28Si differential scattering cross section σ() in the laboratory energy range EL from 50.0 MeV to 142.5 MeV and angular range from 0° to 100° using the LC potential suggested by Lee and Chan. This potential is very successful in explaining the differential cross section σ() at EL = 50.0 and 55.0 MeV in the entire centre of mass angle range reproducing the enhanced back angle oscillations correctly. The LC potential has only seven parameters, including the Coulomb radius parameter, which is much smaller than the number of parameters used in recent calculations on the system. In the light of an excellent fit to the data, we make a detailed analysis of different features of the LC potential and compare it with the typical heavy-ion potential having a Woods-Saxon (WS) form factor used in the analysis of 18O + 58Ni at EL = 60.0 MeV. These features include the behaviour of the real effective potential around grazing partial wave (ℓg), angular momentum (ℓ) dependence of classical deflection function (Θ), reflection function |Sℓ| and the term |1 - Sℓ|2 governing the total partial wave elastic cross section. We also calculate the barrier region resonance positions generated by the partial waves around ℓg. We find that the orbiting phenomenon generated by the flatter, surface transparent effective potential and the resulting coherent behaviour of only a small number of partial waves in the surface region, resulting in the interference of absorptive region and Coulombic region amplitudes, are primarily responsible for back angle oscillations. As a quantum-mechanical consequence of orbiting behaviour, we find close clustering of resonances corresponding to a set of partial waves around ℓg which is the special feature of the LC potential. On the basis of this, we envisage that 16O + 28Si is likely to show large enhanced back angle oscillations at EL = 66.0 and 72.0 MeV. It will be interesting if this is experimentally investigated. © 2006 IOP Publishing Ltd.