A 7–9 MeV isotopic gamma-ray source for detector testing

An isotopic source of high-energy gamma rays has been constructed and tested. The source uses either a long-lived americium–beryllium neutron source or 252Cf to produce fast neutrons, which are moderated in paraffin and then absorbed in metallic nickel. The radiative capture of thermal neutrons in natural metallic Ni produced five prominent gamma-ray energies in the range 7.5–9 MeV, of which the 8.997 MeV line is the strongest by more than a factor of two. The source was optimized for counting rate by measuring gamma-ray energy spectra with a 76 mm diam. NaI detector, then used to test an imaging BGO detector with gamma rays in the energy range 7.5–9 MeV.