Abstract
We have searched for neutrons from the three-body photon-induced reaction {sup 9}Be+{gamma}{yields}{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 {sup 3}He proportional counters embedded in paraffin. Based on energy and intensity calibrations of the accelerator and detector using the {sup 9}Be+{gamma}{yields}{sup 8}Be+n reaction, an upper limit of 93 nb (4{sigma}) 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 {sup 142}Pr 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 0 deg. to 60 deg. 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 {sup 142}Pr beta-ray spectrum could account for the photoneutron yield in the three-body region that had previously been attributed to {sup 142}Pr gamma rays.
Published Version
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