Neutron single particle structure in Sn131 and direct neutron capture cross sections

Recent calculations suggest that the rate of neutron capture by Sn130 has a significant impact on late-time nucleosynthesis in the r process. Direct capture into low-lying bound states is expected to be significant in neutron capture near the N=82 closed shell, so r-process reaction rates may be strongly impacted by the properties of neutron single particle states in this region. In order to investigate these properties, the (d,p) reaction has been studied in inverse kinematics using a 630MeV beam of Sn130 (4.8MeV/u) and a (CD 2) n target. An array of Si strip detectors, including the Silicon Detector Array and an early implementation of the Oak Ridge Rutgers University Barrel Array, was used to detect reaction products. Results for the Sn130(d, p)Sn131 reaction are found to be very similar to those from the previously reported Sn132(d, p)Sn133 reaction. Direct-semidirect (n,γ) cross section calculations, based for the first time on experimental data, are presented. The uncertainties in these cross sections are thus reduced by orders of magnitude from previous estimates. © 2012 American Physical Society

Direct neutron capture cross section on Ge 80 and probing shape coexistence in neutron-rich nuclei

Results are presented from the first neutron-transfer measurement on Ge80 using an exotic beam from the Holifield Radioactive Ion Beam Facility at Oak Ridge National Laboratory. Newly measured spins and spectroscopic factors of low-lying states of Ge81 are determined, and the neutron capture cross section on Ge80 was calculated in a direct-semidirect model to provide a more realistic (n,γ) reaction rate for r-process simulations. Furthermore, a region of shape coexistence around N≈50 is confirmed and implications for the magic nature of Ni78 are discussed