UNIFORM SEMICLASSICAL AND QUANTUM CALCULATIONS OF REGGE-POLE POSITIONS AND RESIDUES FOR COMPLEX OPTICAL NUCLEAR HEAVY-ION POTENTIALS

The first uniform semiclassical (SC) calculations of Regge pole positi ons and residues have been carried out for four complex optical potent ials, which have been used to fit O-16 + Si-28 elastic-scattering data at E(lab) = 55 MeV. In particular, we have extended a SC formalism de veloped for atomic and molecular scatterings to allow for the presence of a long-range Coulomb potential. The SC Regge poles and residues ar e compared with quantum results of Takemasa and Tamura [Phys. Rev. C 1 8, 1282 (1978)], who numerically integrated the radial Schrodinger equ ation. The SC computations show that Takemasa and Tamura missed ten po les. Using a modified version of the quantum computer code REGGE, due to Takemasa, Tamura, and Wolter [Comput. Phys. Commun. 18, 427 (1979)] we have located five of these poles-the remaining poles have residues of modulus < 10(-8). For low values of the Regge pole quantum number n, the SC and quantum pole positions are in close agreement, with larg er differences for the residues. As n increases, the SC results become less accurate. However at high values of n, the quantum results also lose accuracy due to numerical instabilities in the REGGE code. It is demonstrated that the choice of Coulomb interaction-charged sphere or pure Coulomb-can significantly effect the properties of the Regge pole positions and residues.