Structure of 9Be from proton scattering at 180 MeV.

Abstract

Cross section and analyzing power measurements for the scattering of 180 MeV protons are used to investigate the structure of $^{9}\mathrm{Be}$. Data were collected for 24 states below 21 MeV of excitation. Detailed line-shape analysis was used to isolate several broad states. Most notably, the dependence of apparent peak position upon momentum transfer was used to separate the strong resonance listed as 6.76 MeV in standard compilations into two contributions identified as the 7/${2}^{\mathrm{\ensuremath{-}}}$ member of the ground-state rotational band, located at 6.38 MeV, and the 9/${2}^{+}$ weak-coupling state, located at 6.76 MeV. Calculations of proton scattering were made using a density-dependent effective interaction in the local density approximation. The quadrupole contribution to elastic scattering was included in distorted wave Born approximation and found to have an important effect upon the analyzing power. For states dominated by a single multipolarity, neutron transition densities were fitted to (p,p') data and compared with the corresponding proton transition densities fitted to (e,e') data. We find that excitation of the rotational states and the 9/${2}^{+}$ state are essentially isoscalar. Shell model calculations were performed in the full 0\ensuremath{\Elzxh}\ensuremath{\omega} and 1\ensuremath{\Elzxh}\ensuremath{\omega} model spaces. Suggested assignments for most states are made by comparisons of shell model calculations with data for both (p,p') and (e,e'). Similar calculations for analog states observed with the $^{9}\mathrm{Be}$(p,n${)}^{9}$B reaction at 135 MeV support the proposed assignments. Finally, several relatively narrow states are observed between 18 and 21 MeV that are candidates for positive-parity states with T=3/2.