Resonant structures in the ¹⁶O + ²⁰Ne system

Abstract

Gross resonant structures observed in 16O + 20Ne elastic scattering and the 20Ne(16O, 12C)24Mg(g.s.) reaction for 22.8 MeV ≦ Ec.m.(16O + 20Ne) ≦ 38.6 MeV have been studied successfully using an extended optical model and an exact finite-range (EFR) DWBA approach, respectively. The ion-ion potentials employed include both a real parity-dependent interaction and an angular momentum (J) dependent absorptive term. It is demonstrated that the inclusion of both these terms is essential for the prediction of the four gross structures observed in the 16O + 20Ne elastic scattering excitation function at θc.m. = 154°, with each of those structures being modelled as a doublet of even parity plus odd parity shape resonances. The doublet structure is a consequence of the parity-dependent interaction and is enhanced by the J-dependent absorptive form. The 16O + 20Ne elastic scattering angular distributions at Ec.m. = 24.5, 27.9, 31.7, 32.1, 33.0 and 35.5 MeV are also generally well reproduced. The 12C + 24Mg potential is determined by fitting available elastic scattering data, with the constraint that the shape resonances of the 12C + 24Mg interaction overlap approximately the corresponding 16O + 20Ne shape resonances. EFR-DWBA calculations using optical potentials which describe the elastic scattering data do not reproduce the observed resonant gross structures of the 20Ne(16O, 12C)24Mg(g.s.) excitation function at θlab = 13°. However, it is shown that these gross structures, their previously assigned Jπ values and the measured angular distribution data at Ec.m. (16O + 20Ne) = 24.5, 27.9, 31.7, 32.1, 33.0 and 35.5 MeV can be well described by making the optical potentials more surface transparent. This different degree of transparency required to describe the elastic scattering and transfer reaction is discussed. The role of elastic transfer, the sign of the parity-dependent interaction and the possibility of shape resonances with different numbers of nodes are also considered. Show more