Rod pinch radiography source optimization at 2.3 MV

Rod pinch diodes have shown considerable promise as high-brightness flash X-ray sources for penetrating dynamic radiography for a variety of DOE Defense Programs applications. The rod pinch diode uses a small diameter (0.4 - 2 mm) anode rod extended through a cathode aperture. When properly configured, the electron beam from the aperture edge can self-insulate and pinch onto the tip of the rod creating an intense, small X-ray source. Experiments have been performed on Sandia´s SABRE accelerator (2.3MV, 40 /spl Omega/, 60 ns) to optimize the source by maximizing the figure of merit (dose/spot diameter/sup 2/) and minimizing the diode impedance droop. Many diode parameters have been examined including rod diameter, rod length, rod material, cathode aperture diameter, and cathode thickness. The best configuration tested so far uses a 0.5 mm diameter gold rod, a 6 mm rod extension beyond the cathode aperture (diameter = 8 mm), to produce a world record 3.5 rad (filtered dose) at 1 m from a 0.85 mm x-ray spot.