Shielding a monoenergetic photon source for nonproliferation applications analysis

Near-monoenergetic photon sources offer appealing improvements over broad-band bremsstrahlung sources when applied to challenges in nonproliferation efforts. The use of a laser-plasma accelerator offers electrons at the energies needed for multi-MeV Thomson sources in a compact form factor. Because these electrons have energy up to approximately 0.5 GeV, many energetic photons and neutrons are created as they are dumped out of the beam line. This fact creates challenges for performing experiments to demonstrate the advantages of such a photon source for nonproliferation applications in the short term, until effective methods for decelerating the electrons are developed. To mitigate these background particles for laboratory measurements, a system of beam dumps and secondary collimators has been designed. Once background flux is reduced to the lowest practical level, it is compared to the expected flux created by the source photon beam on a lead target. This simulation mimics a nonproliferation application by predicting measured flux off-axis from an interrogated high-Z object as a surrogate for special nuclear material. Background mitigation techniques are also expanded to a mobile interrogation case. These methods allow for demonstration of nonproliferation applications of near-monoenergetic photon sources and future deployment in the field.