Improved ${}^{94}$Mo neutron resonance parameters from neutron capture and transmission measurements at n_TOF and GELINA

Abstract

We report high-resolution measurements of the ${}^{94}\mathrm{Mo}(\mathrm{n},\gamma {)}^{95}\mathrm{Mo}$ cross section in the neutron energy range from a few eV up to about 250 keV, performed at the n_TOF facility (CERN), and of the ${}^{94}\mathrm{Mo}(\mathrm{n},\mathrm{tot})$ cross section up to 32 keV, measured at GELINA (JRC Geel). A combined R-matrix analysis of capture and transmission data yields significantly improved neutron-resonance parameters for ${}^{94}$Mo. A total of 186 resonances were observed in this analysis of which 127 reported here for the first time. The resulting Maxwellian-averaged cross section at stellar temperatures relevant to the slow neutron-capture process (s-process) is approximately 25% lower than previous evaluations and literature values. To assess the astrophysical impact of the revised cross section, we performed s-process nucleosynthesis calculations for low-mass asymptotic giant branch stars. Despite the substantial reduction in the ${}^{94}\mathrm{Mo}(\mathrm{n},\gamma {)}^{95}\mathrm{Mo}$ rate, the final yields vary by only 3-4%. This demonstrates that the isotopic budget of ${}^{94}$Mo in AGB stars is primarily governed by the branching flow at ${}^{94}\mathrm{Nb}$ rather than by the neutron-capture destruction on ${}^{94}$Mo itself. The new cross section thus helps disentangle nuclear cross-section uncertainties from branching-flow effects in the s-process production of ${}^{94}$Mo.