Abstract
Background: The phenomenological optical model has been extensively used to study the nucleon-nucleus scattering process. However, its use in describing the observables for nucleon scattering off light $1p$-shell nuclei has been somewhat limited and less successful. This is a result of their diffuse edges and deformations that complicate fitting the experimental data. Therefore, global optical models usually exclude light nuclei and only consider intermediate and heavy nuclei with mass number $A\ensuremath{\ge}24$.Purpose: We test the effectiveness of a semimicroscopic optical model with channel coupling in describing observables for neutron scattering off nuclei covering a wide mass range from $^{12}\mathrm{C}$ to $^{208}\mathrm{Pb}$ corresponding to neutron incident energies in the range $E=10--30\phantom{\rule{0.28em}{0ex}}\mathrm{MeV}$.Method: The real central part of the optical model is constructed by single folding the density-independent M3Y-Paris bare nucleon-nucleon interaction over the density of the target nucleus. The rest of the potential terms are of Woods-Saxon form or its derivative. The potential parameters are determined by fitting the elastic and inelastic angular distributions in addition to polarization data for neutron scattering from $^{12}\mathrm{C}, ^{16}\mathrm{O}, ^{54}\mathrm{Fe}, ^{58}\mathrm{Ni}, ^{120}\mathrm{Sn}$, and $^{208}\mathrm{Pb}$. In doing so the ground state is coupled to few, low-lying rotational and vibrational excitation channels.Results: Despite considering a wide mass range of nuclei, the model resulted in good descriptions for the elastic data and, at least, the overall features of the inelastic angular distributions and polarization data are reproduced. Our potential depths are expressed as linear functions of energy while, for each target nucleus, the geometric parameters are fixed. This is unlike purely phenomenological optical models which, in many cases, resulted in best-fit parameters that show unclear energy-dependence trends. In addition, the total cross sections predicted using our parameters are in good overall agreement with experiment.Conclusions: The semimicroscopic model based on the M3Y-Paris bare $NN$ interaction succeeded in, at least, reproducing the overall features of the inelastic experimental data. However, the predicted elastic angular distributions are in good agreement with experiment and progressively improved with increasing mass number of the target. Furthermore, the weak energy dependence, introduced into the M3Y-Paris interaction via the knock-on exchange term, led to improving our data fits. Finally, other density-dependent bare $NN$ interactions resulted in potential parameters that showed less systematic behaviors with energy.
Published Version
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