Bayesian calibration of a regional optical potential and uncertainty-quantified predictions for compound nucleus reactions

Abstract

Uncertainty-quantified global optical potential parameterizations are useful for making systematic studies across the nuclear chart and making predictions away from stability. While they generally provide a good description of the reactions on which they were calibrated, predictions can deviate strongly in specific cases and extrapolations incur large uncertainties. We propose a regional optical potential suited for a specific region of the nuclear landscape. We calibrate the potential along isotopic chains to enable both strong data coverage and improved extrapolative power. We modify the Chapel Hill optical potential and the statistical model used previously by Pruitt et al., to perform a Bayesian analysis of elastic scattering of neutrons and protons from zirconium isotopes with improved data coverage. The parameter distributions of our Chapel Hill Regional Potential (CHiRP) are propagated to compound nucleus reaction observables including (n, n'), (n, g) and (n, 2n), which have relevance to various nuclear technology applications. Results are compared to CHUQ, a global calibration of the Chapel Hill potential. The final parameterization of CHiRP differs from CHUQ particularly in the energy and radial dependence of its imaginary components. For elastic scattering, the uncertainties on the observables using CHiRP are smaller than those using CHUQ. CHiRP also provides an improvement over its global counterpart in the agreement with data around 10 MeV, while the regional and global approaches offer similar levels of agreement to elastic data at higher energies. The relative performance of CHiRP and CHUQ when propagating their uncertainty through compound nucleus reaction channels is also reported. The regional potential approach is a viable alternative to global optical model parameterizations for applications that require precise information within a sub-region of the nuclear landscape.