Final Design of a Mobile Pit Verification System

The Mobile Pit Verification System (MPVS) was designed as a “drive by” passive radiation detection system intended to enable a comprehensive, rapid verification and validation of stored nuclear weapon core physics packages containing Special Nuclear Material (SNM), or so-called “weapon pits,” in weapon materials and stockpile storage facilities. This analysis included a synthetic aperture collection approach, and a new gamma ratio methodology for distinguishing between Naturally Occurring Radioactive Materials (NORM) and weapon class SNM materials. Emphasis was placed on the design of a set of tungsten collimators to isolate signals of interest and reduce noise from adjacent sources. This analysis builds upon previous work on source term characterization of weapons grade plutonium (WGPu) and highly enriched uranium (HEU) by Chin, Paul, & Sjoden (2012). Forward and adjoint transport methods using the 3D discrete ordinates code PENTRAN were utilized to characterize the adjoint reaction rates as a function of inter-source spacing, collimation thickness, linear and angular field of view, source age, source type, source geometry, and mobile platform speed. The integrated count was then compared with background radiation and the associated probabilities of detection and false alarm were then computed. This allowed for a minimum number of detectors as a function of energy group to be determined.