Ground-state proton decay of 69Br and implications for the 68Se astrophysical rapid proton-capture process waiting point.

We report on the first direct measurement of the proton separation energy for the proton-unbound nucleus (69)Br. Bypassing the (68)Se waiting point in the rp process is directly related to the 2p-capture rate through (69)Br, which depends exponentially on the proton separation energy. We find a proton separation energy for (69)Br of Sp((69)Br )= -785(-40)(+34) keV; this is less bound compared to previous predictions which have relied on uncertain theoretical calculations. The influence of the extracted proton separation energy on the rp process occurring in type I x-ray bursts is examined within the context of a one-zone burst model.

Mechanisms in knockout reactions.

We report the first detailed study of the relative importance of the stripping and diffraction mechanisms involved in nucleon knockout reactions, by the use of a coincidence measurement of the residue and fast proton following one-proton knockout reactions. The measurements used the S800 spectrograph in combination with the HiRA detector array at the NSCL. Results for the reactions 9Be(9C,8B+X)Y and 9Be(8B,7Be+X)Y are presented and compared with theoretical predictions for the two reaction mechanisms calculated using the eikonal model. The data show a clear distinction between the stripping and diffraction mechanisms and the measured relative proportions are very well reproduced by the reaction theory. This agreement adds support to the results of knockout reaction analyses and their applications to the spectroscopy of rare isotopes.

Isotopic dependence of the nuclear caloric curve.

The A/Z dependence of projectile fragmentation at relativistic energies has been studied with the ALADIN forward spectrometer at SIS. A stable beam of (124)Sn and radioactive beams of (124)La and (107)Sn at 600 MeV per nucleon have been used in order to explore a wide range of isotopic compositions. Chemical freeze-out temperatures are found to be nearly invariant with respect to the A/Z of the produced spectator sources, consistent with predictions for expanded systems. Small Coulomb effects (DeltaT approximately 0.6 MeV) appear for residue production near the onset of multifragmentation.

Neutron and proton transverse emission ratio measurements and the density dependence of the asymmetry term of the nuclear equation of state.

Recent measurements of preequilibrium neutron and proton transverse emission from (112,124)Sn+(112,124)Sn reactions at 50 MeV/A have been completed at the National Superconducting Cyclotron Laboratory. Free nucleon transverse emission ratios are compared to those of A=3 mirror nuclei. Comparisons are made to Boltzmann-Uehling-Uhlenbeck (BUU) transport calculations and conclusions concerning the density dependence of the asymmetry term of the nuclear equation of state at subnuclear densities are made. Comparison to BUU model predictions indicate a density dependence of the asymmetry energy that is closer to a form in which the asymmetry energy increases as the square root of the density for the density region studied. A coalescent-invariant analysis is introduced as a means of reducing suggested difficulties with cluster emission in total nucleon emission.

Shell structure of the near-dripline nucleus 23O.

Breakup reactions were used to study the ground-state configuration of the neutron-rich isotope 23O. The 22O fragments produced in one-nucleon removal from 23O at 938 MeV/nucleon in a carbon target were detected in coincidence with deexciting gamma rays. The widths of the longitudinal momentum distributions of the 22O fragments and the one-neutron removal cross sections were interpreted in the framework of a simple theoretical model which favors the assignment of Ipi = 1/2+ to the 23O ground state.