Prompt Neutron Multiplicity Measurements with Portable Detectors

Mobile detection of kilogram quantities of SNM during maritime transportation is a challenging problem for the Department of Homeland Security (DHS). Counting neutrons emitted by the SNM and partitioning them from the background neutrons of various origins is the most effective passive means of detecting the SNM. Unfortunately, neutron detection, counting and partitioning in a maritime environment is complex due to the presence of spallation neutrons (commonly known as. ship effect.) and to the complicated nature of the neutron scattering in that environment. This work studied the possibilities of building a prototype neutron detector using boron-10 (B-10) as the converter in a novel form factor called. straws. that would address the above problem by looking into the details of multiplicity distributions of neutrons originating from a fissioning source. Currently, commercially manufactured Fission Meters (FM) are available that separate cosmic neutrons from non-cosmic neutrons and quantitatively determine the strength of a fissioning source; however, these FMs use He-3, which is becoming increasingly difficult to procure; also the size and weight of an FM is not conducive to manual neutron detection operations in a maritime environment. The current project may provide a near-term solution to the crisis that has arisen from the global scarcity of He-3 by offering a viable alternative to the FM. The prototype provides a large area, efficient, lightweight, more granular neutron responsive detection surface (to facilitate imaging) to enhance the ease of application of FMs.