Measurement of the 100Mo(α, xn) cross section at weak r-process energies

The weak r process in neutrino-driven winds following a core-collapse supernova is thought to contribute to the cosmic abundances of the first r-process peak elements between Se and Ag. Sensitivity studies have found that the early nucleosynthesis in the weak r process is primarily driven by (alpha, xn) reactions due to the high temperatures, and that current nuclear physics uncertainties in the (alpha, xn) rates result in significant uncertainties of the calculated abundances. The weak r-process path proceeds several nuclei away from stability where (alpha, xn) reaction cross sections have not yet been measured. In this paper we report the( 100)Mo(alpha, xn) cross section (between 8.9 and 13.2 MeV in the center of mass, corresponding to 3.5-6.8 GK) in inverse kinematics using the Multi-Sampling Ionization Chamber (MUSIC) detector at the Argonne Tandem Linac Accelerator System (ATLAS) facility. With this first measurement of the Mo-100(alpha, xn) cross section, we have demonstrated the ability of MUSIC to measure (alpha, xn) cross sections for A up to 100, therefore paving the way for further measurements with radioactive beams at ATLAS or the Facility for Rare Isotope Beams.