Advances in acoustically-tensioned metastable detector neutron detection technology

Abstract

Nuclear security, the prevention of special nuclear material (SNM) smuggling, at borders and ports has been described as one of the 21st century grand challenges. Currently, thermal neutron detectors (a majority of which are He-3 detectors), are used to monitor for neutrons emitted from special nuclear materials. He-3 neutron absorption cross-sections are ∼103 times higher for thermal vs fast neutrons; as such, moderated He-3 detectors must suffer from reduced efficiency (due to scattering and absorption in moderators) for detection of fast neutrons emitted from fission of SNMs. Development of a real-time high-efficiency gamma/beta blind, directionality-determining thermal and fast neutron monitoring system without need for bulky moderation is needed to allow for optimal SNM monitoring. The previously developed economical acoustically tensioned metastable fluid detector (E-ATMFD(Ver.0), offered all of these capabilities but exhibited low (∼0.01–0.05%) efficiencies than conventional neutron monitors. Design optimization guided via coupled multiphysics-neutron transport simulation tools, together with devising a figure of merit algorithm, experimental validation work with various reflector shapes, and a novel detection fluid “DFP”, the direct drive E-ATMFD(Ver.1) architecture was devised and demonstrated to offer ∼5 to 27x improvement in neutron detection efficiency. Using borated DFP mixture version E-ATMFD(Ver.1B), epithermal to fast neutron detection capabilities were demonstrated — effectively extending the sensitivity to all energies of neutrons and increasing the efficiency by another factor of up to ∼2.5. Further research included development of a novel frequency sweep-cum-rate drive mode to successfully operate multiple E-ATMFDs simultaneously from a single power source; resulting in a further 4x detection efficiency improvement from enhanced scattering and electromagnetic coupling — showing potential for enabling large array mode SNM interrogation.