Polarization asymmetries in the Be 9 (γ,n0) reaction

Measurements of the Be9(γ,n0) reaction were performed using nearly 100% linearly polarized, high-intensity, and nearly monoenergetic γ-ray beams having energies between 5.5 and 15.5 MeV at the High Intensity γ-ray Source located at Duke University and Triangle Universities Nuclear Laboratory. Eighteen liquid scintillator detectors were used to measure neutron yields parallel and perpendicular to the plane of beam polarization. Polarization asymmetries, which are the differences between yields observed in detectors located in-plane and out-of-plane divided by their sums, were measured for the neutrons which left the residual nucleus (Be8) in its ground state, termed the n0 group. Asymmetries between 0.4 to 0.7 were discovered over this energy region in addition to a clear trend of increasing asymmetries with increasing beam energy. A prediction of the polarization asymmetry based on a pure E1 direct capture model shows good agreement with the experimental measurements. These data and the prediction could be of interest for methods that rely on neutron measurements following photofission to identify the presence of special nuclear material.

Duke Scholars

Author Diane M Markoff Physics