Photoneutron Reactions in 18O

Abstract

Photoneutron energy spectra from 18O have been measured by time-of-flight spectroscopy at bremsstrahlung endpoint energies from 11 to 18 MeV in 1 MeV steps to obtain the (γ, n0) and (γ, n1) differential cross sections. The ground state photoneutron cross section contains at least 8 major resonances in the region from 10 to 17 MeV and has an average value of 100 μb/sr. The cross section to the first excited state of 17O contains only two major resonances, at 11.4 and 14.4 MeV, and the average cross section in the region from 11 to 16 MeV is about 40 μb/sr. Of particular interest is a resonance at 14.4 MeV which appears to reflect a simple excitation of one of the valence neutrons to the 2p3/2 state. Analysis of the (γ, n0) and (γ, n1) cross sections for this continuum state leads to estimates of the configuration amplitudes of the 2s1/2 and 1d5/2 components of this state to be 0.62 ± 0.06 and 0.78 ± 0.08 respectively and the ratio of the (2s1/2)2 to (1d5/2)2 amplitudes in the ground state of 18O to be 0.39 ± 0.02.