Determination of the asymmetry term strength in the n–A elastic scattering process using a nonlocal optical model

Abstract

In previous works, the imaginary surface and (or) the imaginary volume depths of the optical potential were parametrized as linear functions of the projectile’s incident energy and neutron-proton asymmetry (N – Z)/A of the target nucleus. However, the obtained asymmetry strength parameters were not robust nor unique. In this work, we determine values for the strength parameters by simultaneously fitting 38 angular distribution data sets corresponding to neutron elastic scattering off chains of isotopes. For each isotopic chain, we considered the data sets that are measured at the same energy. This minimises the effect of the known energy dependence of the optical model and projects the dependence on the asymmetry term, which in turn leads to more reliable values of the strength parameters. To demonstrate the significance of the obtained strength values, we use the model to predict elastic angular distributions for neutron scattering off nuclei not considered in the χ2 analysis. Our theoretical angular distributions are in good agreement with the measured data and are also comparable to the predictions of local global models. In addition, our predicted total elastic and total reaction cross sections are in fair overall agreement with experiment. An additional result of this work is the determination of a global set of nonlocal parameters that describe neutron elastic scattering off nuclei that fall in the mass range 24 ≤ A ≤ 208 corresponding to incident neutron energies between ≈10–30 MeV.