LLNL, Livermore, California, USA
Lawrence Livermore National Lab is developing an intense, high-brightness fast neutron source to create high resolution neutron radiographs and images. An intense source (1011 n/s/sr at 0 degrees) of fast neutrons (10 MeV) allows: penetrating very thick, dense objects; maintaining high scintillator response efficiency; and remaining below the air activation threshold for (n,p) reactions. Fast neutrons will be produced using a pulsed 7 MeV, 300 microamp average-current commercial ion accelerator that will deliver deuterons to a 3 atmosphere deuterium gas cell. To achieve high resolution, a small (1.5 mm diameter) beam spot size will be used, and to reduce scattering from lower energy neutrons, a transmission gas cell will be used to produce a quasi-monoenergetic neutron beam. Because of the high power density of such a tightly focused, modest-energy ion beam, the gas target is a major engineering challenge that combines a 'windowless' rotating aperture, a rotary valve to meter cross-flowing high pressure gases, a novel gas beam stop, and recirculating gas compressor systems. A summary of the progress of the system design and building effort shall be presented.
