Theoretical radiation-dose profiles for annular-beam flash γ-ray sources

This report investigates the bremsstrahlung radiation fields expected from intense, pulsed annular-beams of electrons over the range of 5 to 20 MeV. Explored are fields from a single beam (used to generate small-area irradiations) and fields from multiple beams (used to generate large-area irradiations). The geometries assumed are characteristic of beam configurations presently being studied at Sandia National Laboratories. The analysis shows that near-target irradiations provide efficient use of the available radiation without introducing significant nonuniformities to the radiation pattern. Efficient large-area sources can be generated by distributing the beams over an area comparable to that being irradiated. Backing away from the target where the γ-rays are generated, on the other hand, is an inefficient method for generating a large-area irradiation. By increasing the kinetic energy of the beam, higher doses are possible over comparable areas; specifically, over the investigated range, increasing the energy 5 MeV roughly doubles the useful dose