Differential polarization of photoneutrons from 16O

Abstract

The differential polarization of ground-state photoneutrons from 16O has been determined at five angles at energies below 26 MeV. The polarization was measured by observing the asymmetry in the elastic scattering of the photoneutrons from either a liquid helium or a graphite target. The neutron energies were measured with a time-of-flight spectrometer; the resolution was 300 ps m-1. Systematic errors were minimized by using a neutron spin-precession solenoid. The values of the s-, p-, d- and f-wave amplitudes and phases of the reaction matrix elements have been deduced. The results are compared with those obtained from the 15N(p, gamma 0)16O reaction and with the predictions of various theoretical models. The observed energy dependence of the neutron polarization, and the energy dependence of the amplitudes and phases are not well accounted for by any currently available model.