Search For The Three-Body Photodisintegration Of Be

We have searched for neutrons from the three-body photon-induced reaction Be-9+gamma-->alpha+alpha+n using bremsstrahlung produced by electrons from a 2-MV Van de Graaff on a gold target. The target was located within a block of beryllium surrounded by an array of He-3 proportional counters embedded in paraffin. Based on energy and intensity calibrations of the accelerator and detector using the Be-9+gamma-->Be-8+n reaction, an upper limit of 93 nb (4sigma) was placed on the cross section for neutron production between the three-body and two-body thresholds. This value is substantially below a previous experimental result using photoexcitation by Pr-142 gamma rays and also below an earlier theoretical estimate. Bremsstrahlung spectra from the gold target were also measured in a NaI(Tl) detector at electron energies from 1.7 to 2.0 MeV and angles of 0degrees to 60degrees with respect to the beam axis. An analysis of photons above the 1665-keV two-body threshold shows that bremsstrahlung due to beta rays between 1665 keV and the 2160-keV end point of the Pr-142 beta-ray spectrum could account for the photoneutron yield in the three-body region that had previously been attributed to Pr-142 gamma rays.