Polarization of Protons Elastically Scattered by Oxygen

Abstract

Measurements of the polarization of protons elastically scattered by oxygen have been made between 2 and 12 MeV by double scattering using gas targets. Scattering by helium at 46\ifmmode^\circ\else\textdegree\fi{} was used as the polarization analyzer for most of the work. In addition, four angular distributions of the cross section were measured between 2.5 and 3.8 MeV. The experimental results show that away from the known sharp resonances at 2.66 and 3.47 MeV the polarization changes slowly with energy between 2 and 5 MeV. At 3 MeV the polarization is negative at forward angles and positive at back angles, the observed extrema being -0.14\ifmmode\pm\else\textpm\fi{}0.02 at 45\ifmmode^\circ\else\textdegree\fi{} and 0.43\ifmmode\pm\else\textpm\fi{}0.03 at 115\ifmmode^\circ\else\textdegree\fi{}. At higher energies the pronounced resonance structure causes rapid fluctuations of the polarization with energy. Angular distributions of the polarization were measured at eleven energies away from sharp resonances. At 10.7 MeV the observed extrema in the polarization are -0.88\ifmmode\pm\else\textpm\fi{}0.04 at 50\ifmmode^\circ\else\textdegree\fi{}, 0.92\ifmmode\pm\else\textpm\fi{}0.04 at 65\ifmmode^\circ\else\textdegree\fi{}. and -0.83\ifmmode\pm\else\textpm\fi{}0.03 at 133\ifmmode^\circ\else\textdegree\fi{}. A phase shift analysis of the polarization and cross section was made between 2 and 5 MeV and at four energies between 5 and 7 MeV. The phase shifts obtained differ from those of Salisbury and Richards by less than 10 deg. The measured angular distributions of the polarization between 8 and 12 MeV are also compared with the predictions of the optical model. New results of the polarization for $p\ensuremath{-}\ensuremath{\alpha}$ scattering and $p$-C scattering between 2 and 4 MeV are also reported.