Activation thick target yield measurement of Mo100(α,n)Ru103 for studying the weak r -process nucleosynthesis

Abstract

Background: Light ($30\ensuremath{\le}Z\ensuremath{\le}45$) neutron-rich isotopes are thought to be synthesized in the neutrino-driven ejecta of core-collapse supernovae explosions via the weak $r$ process. Recent nucleosynthesis studies have demonstrated that $(\ensuremath{\alpha},xn)$ reactions play a particularly important role in the production of these isotopes. $\ensuremath{\alpha}$-nucleus optical model potentials ($\ensuremath{\alpha}$-OMPs) are used to model this nucleosynthesis scenario.Purpose: The different $\ensuremath{\alpha}$-OMP model parameters can affect the calculated cross sections by more than an order of magnitude in the relevant energy regions, which affects the production of light neutron-rich isotopes. Consequently, to constrain the astrophysical conditions characterizing the supernovae ejecta, the uncertainty of the nuclear physics input has to be reduced.Methods: The cross section of the $^{100}\mathrm{Mo}(\ensuremath{\alpha},n)^{103}\mathrm{Ru}$ reaction was measured by means of the activation method. 0.5 mm thick molybdenum disks were irradiated with ${E}_{\ensuremath{\alpha}}$ = 7.0 to ${E}_{\ensuremath{\alpha}}$ = 13.0 MeV $\ensuremath{\alpha}$ beams. Thick target yields and reaction cross sections were determined via $\ensuremath{\gamma}$-ray spectroscopy.Results: Cross sections at several energies below the Coulomb barrier were measured, reaching the astrophysically relevant energy region. Large discrepancies between the experimental values and statistical model predictions calculated using the well-known $\ensuremath{\alpha}$-OMPs were found. The measured cross section data could be excellently described by the Atomki-V2 potential. Therefore, this $\ensuremath{\alpha}$-OMP was used to derive the astrophysical reaction rates as a function of temperature.Conclusions: The successful reproduction of the measured cross sections in a wide energy region confirm the reliability of the Atomki-V2 potential. The usage of the new $^{100}\mathrm{Mo}(\ensuremath{\alpha},n)^{103}\mathrm{Ru}$ experimental data along with the Atomki-V2 potential reduces the nuclear uncertainties of the weak $r$-process production yields of nuclei with $36\ensuremath{\le}Z\ensuremath{\le}50$ to a marginal level.