Acoustically tensioned metastable fluid detector system for directional neutron detection & imaging of special nuclear material
A critical gap in national security concerns the inability to efficiently detect and identify problematic quantities of special nuclear material (SNM). These materials, specifically uranium and plutonium, emit neutrons via spontaneous and induced fission. Unlike other forms of radiation produced by SNM (e.g. gamma rays), copious and penetrating neutron emission is unique to fissionable material and is therefore advantageous for detecting SNMs. Directional neutron detection and source positioning offers improved detection speeds when compared to traditional proximity searching and the ability to image the neutron source shape, size, and strength in near real time. The development of one such transformational direction-position sensing neutron detector for the detection of SNM is the Directional Acoustically Tensioned Metastable Fluid Detector (D-ATMFD). Tensioned Metastable Fluid Detector systems are capable of detecting neutrons over 8 orders of magnitude in energy, with over 90% intrinsic efficiencies, operate completely insensitive to gammas and non-neutron cosmic background, ascertain directional and positional information on both thermal and fast neutrons (a capability currently unmatched by any detector system), and represent a significant cost reduction over comparable systems (e.g. $50-$1K vs. $5K->$200K). This work presents major advancements that provide the accuracy and precision of ascertaining directionality and source imaging information utilizing enhanced signal processing-cum-signal analysis, refined computational algorithms, and on demand enlargement of the detector sensitive volume. Advancements in the development of the D-ATMFD were accomplished utilizing a combination of experimentation and theoretical modeling. Modeling methodologies include Monte-Carlo based nuclear particle transport using MCNP5 and MCNP-PoliMi and complex multi-physics based assessments accounting for acoustic, structural, and electromagnetic coupling of the D-AMTFD system via COMSOL's Multi-physics simulation platform. Benchmarking and qualifications studies were successfully conducted with simulant SNM neutron sources (239Pu-Be and 252Cf). These results show that the D-ATMFD system, in its current configuration, is capable of locating an IAEA significant quantity of reactor grade plutonium in a shipping container at 25 m to within 16.4° with 68% confidence in only 2 minutes. SNM source imaging (shape and position) with two D-ATMFD sensors was experimentally demonstrated and validated via MCNP-PoliMi model simulations. Full-scope 3-D directionality monitoring assessments have been addressed (both experimentally and via MCNP-PoliMi simulations) using two (cylindrical) D-ATMFDs and a single spherical design D-ATMFD. Studies for extending the fast neutron direction-position-imaging capabilities for shielded SNM scenarios involving thermal neutron based monitoring also addressed and assessed with encouraging results. Possible applications for a myriad of field-relevant situations are recommended.^
Rusi P. Taleyarkhan, Purdue University.
Nuclear engineering|Nuclear physics and radiation