Photoneutrons from 20Ne

Photoneutron energy distributions from a target of liquid neon have been measured at 90° by time of flight for bremsstrahlung endpoint energies increasing in 1 MeV steps from 19 to 32 MeV. The differential ground state cross section for the major (91%) isotope 20 Ne has been obtained, together with an estimate of the strength of transitions to excited states of 19 Ne. Six photoneutron groups are observed, reflecting photon absorption which correlates excellently with existing photoproton data, although the absolute cross section is about 10% smaller.It is noted that the giant dipole resonance, estimated by combining the photoneutron and photoproton data, is centered at approximately 20 MeV, which is anomalously low, and that the integrated cross section up to 28 MeV exhausts only half of the dipole sum.