Si28(p, p′γ)Angular Correlations

Abstract

Angular correlations have been measured between protons scattered inelastically from a ${\mathrm{Si}}^{28}$ target and the decay gamma rays from the 1.78-Mev first excited state of the target nuclei. The incident proton bombarding energy was varied between 5.8 Mev and 7.0 Mev. The angular correlation experiments were performed for proton detector angles of 37\ifmmode^\circ\else\textdegree\fi{}, 60\ifmmode^\circ\else\textdegree\fi{}, 90\ifmmode^\circ\else\textdegree\fi{}, and 120\ifmmode^\circ\else\textdegree\fi{}. The measured angular correlation functions are all of the form $A+B{sin}^{2}[2(\ensuremath{\theta}\ensuremath{-}{\ensuremath{\theta}}_{0})]$, where ${\ensuremath{\theta}}_{0}$ is the axis of symmetry. When the incident proton beam energy was 7.0 Mev, the symmetry direction was found to be 90\ifmmode^\circ\else\textdegree\fi{} (center of mass) independent of the proton detector angle. These results agree with the prediction of a compound-nucleus theory. This suggests the existence of a strong compound nucleus resonance in ${\mathrm{P}}^{29}$ at an excitation energy of 9.6 Mev. For lower proton beam energies, the symmetry direction ${\ensuremath{\theta}}_{0}$ shifts with a change in the proton detector angle or a change in the proton beam energy. These results are consistent with a direct-reaction mechanism.