The Rp-Process Waiting-Point Nucleus 68se and Its Astrophysical Implications

Precise mass measurements of nuclei along the N = Z line are important input parameters for simulations of the rp-process. Of particular interest is the mass of the Se-68(34)34 rp-process waiting point nucleus for determining the possibility of a two-proton capture branch bypassing its slow P-decay. The mass of Se-68 was measured via the beta-decay endpoint. Se-68 was produced by the C-12(Ni-58, 2n)Se-68 reaction and subsequently implanted onto a moving tape system using the fragment mass analyzer at the ATLAS facility of Argonne National Laboratory. A mass excess value of (-54189 +/- 240) keV was determined from the beta-endpoint measurement of Q(EC) = 4710(200) keV. Evaluations of proton separation energies based on the measured mass were used in a one zone type I X-ray burst model. It is concluded that the N = Z = 34 isotope Se-68 is a waiting point for the rp-process. (C) 2004 Elsevier B.V. All rights reserved.