Active detection of shielded special nuclear material - Dec 2012 AWE/NRL steel shielded campaign EJ301 liquid scintillation detector analysis

An ongoing programme investigating the active detection of special nuclear material (SNM) is being undertaken by the Atomic Weapons Establishment (AWE) in collaboration with the Naval Research Laboratory (NRL). As part of this programme, the NRL Mercury IVA was operated in negative polarity mode to produce an 8 MeV endpoint Bremsstrahlung spectrum, which in turn was used to induce photofission in a depleted uranium (DU) sample. Twenty-six experiments were fielded in March 2011 and good data was obtained for high-Z (lead) and hydrogenous (borated polyethylene) shielding configurations where a positive detection was made up to the maximum shielding tested, 75 g/cm2. In December 2012 further experiments were conducted to directly determine performance through high-Z (steel) shielding at the same facility. With over 80 detectors fielded on more than 70 experiments, this further experimental series represents a step change in performance evaluation of pulsed power driven active detection. We report on analysis of the six liquid scintillation detectors (Eljen 301) which demonstrated a positive detection (>5 σ above background) at the highest shielding level tested.