Photo-Neutron Thresholds of Beryllium and Deuterium

The photo-neutron thresholds of beryllium and deuterium have been measured by comparison with the Li⁷(p,n) threshold. For this purpose an electrostatic generator was used in which an electron beam and a positive ion beam were established simultaneously. Accurate control and measurement of the generator voltage was obtained by using an electrostatic analyzer on the H₂⁺ component of the ion beam. Because the Li⁷(p,n) threshold lies between the Be⁹(γ,n) and D(γ,n) thresholds, errors in extrapolation should be small. The electron beam was accelerated from ground to the accurately known potential of the high voltage electrode where x-rays were produced for the photo-disintegration process. From the photo-neutron thresholds the neutron binding energies of beryllium and deuterium were found to be 1.666±{}0.002 and 2.226±{}0.003 Mev, respectively.