Nature of potential families from elastic ¹⁶O + ¹⁶O rainbow scattering*

Abstract

The experimental differential cross-sections of 16 O + 16 O elastic scattering in the energy range 75 MeV E lab 1120 MeV are analysed using families of non-monotonic (NM) shallow nucleus-nucleus potential in the framework of the optical model. The experimental data is reproduced successfully using six families of NM potentials. It is found that all families converge at 350 MeV. The clear indication of the convergence of the potential families at 350 MeV conforms to the Goldberg criterion concerning the removal of discrete ambiguities even for the shallow NM potential. The study further suggests that the energy of convergence heralds the occurrence of the primary rainbow at that incident energy.

16O + 16O cluster states and their fusion to 32S: A non-monotonic potential description

“…The lowest bound molecular band is expected to have the simplest molecular dynamics and to serve as a key to understand the quasi-molecular bands in the SD and VD configurations of 32 S. Successes of the NM nucleus-nucleus potential have stimulated us to explore the 16 O + 16 O cluster bands and their fusion to 32 S in a simple OM using the NM potentials generated from the EDF theory of BCD. To do this we need good 16 O + 16 O interaction potentials, completely free of discrete ambiguities and, ideally, free of continuous ambiguities as well [28,29,31]. EDF-derived NM potentials are good at lower energies, being most accurate at the zero excitation energy E x = 0.0 MeV of the composite nucleus as detailed in [29].…”

“…The CS data are analyzed using the code SFRESCO which incorporates the coupled-channels code FRESCO2.5 [57] and the χ 2 minimization code MINUIT [58]. Details of the fitting strategy are given in [10,28,29]. Special care has been taken to keep the imaginary part shallow enough [39,59] to contain the continuous ambiguities associated with the real-imaginary parts of the optical potential (OP) and to maintain adequate transparency of the scattering medium to support the refractive features including the nuclear rainbow.…”

“…The NM nucleus-nucleus potential has been found [28,29] to obey the Goldberg criterion [30] for eliminating high energy discrete ambiguities and also explicitly reveals the multiple potential families at lower incident energies.…”

“…The potential families [28,29,31] provide an excellent description of experimental data spanning a wide angular range. They are also [28,29] useful indicators of non-elastic processes and perform similarly in describing elastic scattering data.…”

“…We apply the non-elastic excitations of the deeper NM potential families [28] in locating the Pauli allowed 16 O + 16 O cluster states [2,5,32] of 32 S after rejecting the unphysical bound states (any that are present get removed in the equivalent shallower potential family [33,34]). We also intend to reproduce the experimental 16 O + 16 O fusion cross-sections (FCSs) in the energy range 12-31 MeV where the experimental data [35] exhibit a sharp downward trend close to sub-barrier energies of astrophysical interest [36,37].…”