Constraining nuclear properties in Mo94 via a Nb93(p,γ)Mo94 total cross section measurement

Abstract

Background: The nucleosynthesis of the group of neutron-deficient $p$ nuclei remains an unsolved puzzle in nuclear astrophysics. Among these nuclei, $^{94}\mathrm{Mo}$ is one of the most abundant and is notoriously underproduced in theoretical network calculations. In these networks, the respective cross sections and reaction rates play a crucial role. Since many reactions of astrophysical relevance are not accessible in the laboratory, a global and robust theoretical framework is required to provide reliable predictions.Purpose: Extending the experimental database on the one hand and direct or indirect studies of the respective nuclear physics properties on the other hand are the key tasks of experimental nuclear astrophysics. For this purpose, total cross sections of the $^{93}\mathrm{Nb}(p,\ensuremath{\gamma})^{94}\mathrm{Mo}$ reaction have been measured at proton energies between 2.0 and 5.0 MeV.Methods: In-beam $\ensuremath{\gamma}$-ray spectroscopy has been utilized to measure total cross sections. In general, the total cross sections depend strongly on the $\ensuremath{\gamma}$-ray decay widths in $^{94}\mathrm{Mo}$, which are derived from the $\ensuremath{\gamma}$-ray strength function and the nuclear level density. In our analysis we use a Bayesian optimization analysis to disentangle the effects of the $\ensuremath{\gamma}$-ray strength function and the nuclear level density in $^{94}\mathrm{Mo}$.Results: The total cross-section results reveal a significant discrepancy with respect to formerly published values. We propose parametrizations for the nuclear level density in $^{94}\mathrm{Mo}$ based on the microscopic level densities from Hartree-Fock-Bogoliubov calculations. Moreover, we present $\ensuremath{\gamma}$-ray strength functions for the $E1$ and $M1$ mode in $^{94}\mathrm{Mo}$ that reveal a low-energy enhancement for $M1$ radiation and agree nicely with previous results.Conclusions: A model-independent approach to study $E1$ and $M1$ strength functions has been presented. In general, radiative capture cross sections are a well-suited tool to constrain the reaction rates in reaction networks but also provide insight into the statistical $\ensuremath{\gamma}$-decay behavior of atomic nuclei.