Evidence for a Giant Quadrupole Resonance in Oxygen-16

Abstract

We calculate the angular distribution and polarization of the photoneutrons from ${\mathrm{O}}^{16}$ in the giant-dipole region. We have to supplement our $E1\mathrm{}$ amplitudes, which were obtained previously, with large phenomenological $E2\mathrm{}$ amplitudes; we interpret this as evidence for a giant quadrupole resonance. We show that the importance of $E2\mathrm{}$ amplitudes makes the current data analysis in $E1\mathrm{}$ approximation very doubtful. The assumed $E2\mathrm{}$ resonance is also shown to be easily detected experimentally.