Photoneutron Reactions in ¹⁸O

Abstract

Photoneutron energy spectra from 18 O 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, n 0 ) and (γ, n 1 ) 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 17 O 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 2p 3/2 state. Analysis of the (γ, n 0 ) and (γ, n 1 ) cross sections for this continuum state leads to estimates of the configuration amplitudes of the 2s 1/2 and 1d 5/2 components of this state to be 0.62 ± 0.06 and 0.78 ± 0.08 respectively and the ratio of the (2s 1/2 ) 2 to (1d 5/2 ) 2 amplitudes in the ground state of 18 O to be 0.39 ± 0.02.