Neutron Single Particle Structure in 131Sn and Direct Neutron Capture Cross Sections

Recent calculations suggest that the rate of neutron capture by Sn-130 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 630 MeV beam of Sn-130 (4.8 MeV/u) and a (CD2)(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 Sn-130(d, p)Sn-131 reaction are found to be very similar to those from the previously reported Sn-132(d, p)Sn-133 reaction. Direct-semidirect (n, gamma) 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.