O16(γ, p)N15Angular Distributions over the Energy Range 21-33 MeV

Abstract

Energy and angular distributions of photoprotons from ${\mathrm{O}}^{16}$ have been measured using 33-MeV bremsstrahlung from an electron synchrotron. A relative cross section is obtained for photoproton transitions to the ground state of ${\mathrm{N}}^{15}$ in the energy interval of 27-33 MeV. Below 27 MeV, the data include protons from higher-lying levels decaying through excited states, preventing extraction of a valid cross section for this region. Angular distribution data are analyzed in terms of Legendre polynomials. The anisotropy parameter ${A}_{2}$ has the value of -0.55\ifmmode\pm\else\textpm\fi{}0.2 over the entire energy range, very near the expected value for $d$-wave proton emission from a dipole state. The asymmetry parameters ${A}_{1}$ and ${A}_{3}$ both increase in absolute value to a maximum at 30.5 MeV. Observed fluctuations in ${A}_{1}$ and ${A}_{2}$ are well correlated with known resonances in the cross section. The data indicate a broad region of moderate quadrupole strength extending to the upper energy limit of the experiment.