Recent halo star abundance observations exhibit an important feature of consequence to the rprocess: the presence of a main r-process between the second and third peaks which is consistent among halo stars. We explore fission cycling and steady-β flow as the driving mechanisms behind this feature. The presence of fission cycling during the r-process can account for nucleosynthesis yields between the second and third peaks, whereas the presence of steady-β flow can account for consistent r-process patterns, robust under small variations in astrophysical conditions. We employ the neutrino-driven wind of the core-collapse supernova to examine fission cycling and steady-β flow in the r-process. As the traditional neutrino-driven wind model does not produce the required very neutron-rich conditions for these mechanisms, we examine changes to the neutrino physics necessary for fission cycling to occur in the neutrino-driven wind environment, and we explore under what conditions steady-β flow is obtained.

We investigate the impact of neutron capture rates near the A = 130 peak on the r-process abundance pattern. We show that these capture rates can alter the abundances of individual nuclear species, not only in the region of A = 130 peak, but also throughout the abundance pattern. We discuss the nonequilibrium processes that produce these abundance changes and determine which capture rates have the most significant impact. PACS numbers: 26.30.Hj,26.50.+x 131

Abstract. We examine the role of neutron capture on 130Sn during r-process freezeout in the neutrino-driven wind environment of the core-collapse supernova. We find that the global r-process abundance pattern is sensitive to the magnitude of the neutron capture cross section of Sn, but also a shift in the distribution of material in the rare earth and third peak regions.arXiv:0806.3895v1 [nucl-th]

We investigate nucleosynthesis in the supernovae post-core bounce neutrino-driven wind environment in the presence of active-sterile neutrino transformation. We consider active-sterile neutrino oscillations for a range of mixing parameters: vacuum mass-squared differences of 0.1 eV 2 ≤ δm 2 ≤ 100 eV 2 , and vacuum mixing angles of sin 2 2θv ≥ 10 −4 . We find a consistent r-process pattern for a large range of mixing parameters that is in rough agreement with the halo star CS 22892-052 abundances and the pattern shape is determined by fission cycling. We find that the allowed region for the formation of the r-process peaks overlaps the LSND and NSBL (3+1) allowed region.

No abstract