Year
2012
Abstract
Most current radiation portal monitors (RPMs) use neutron detectors based upon 3He-filled gas proportional counters. 3He is in shortsupply in the world and continuesto decline in availability. Concurrent with the decline in gas is a disproportionate increase in the cost of available gas. It is therefore desirable to find substitutes for the 3He with technologiesthat will effect minimal changes to currently deployed systems and provide equivalent effectivenessin neutron detection. This project investigatesthe feasibility of BF3 as a substitute for the 3He in configurations that can be readily installed in currently deployed systems. In response to this 3He shortage, the U.S. Department of Homeland Security’s (DHS), Domestic Nuclear Detection Office (DNDO), Product Acquisition and Deployment Directorate (PADD) commissioned Brookhaven National Laboratory (BNL) to construct and test a boron tri-fluoride (BF3) based neutron detection module (NDM). The NDM was required to meet specific criteria as outlined in a DNDO Functional Requirements Document (FRD) [1]. The detector was to be built utilizing (as much as practicable) off the shelf components and have the same exterior dimensions as current NDMs so that they can fit into existing portal monitor enclosures. The module was mounted in the standard Radiation Portal Monitor (RPM) NEMA enclosure inside the standard steel shroud, and shipped to the Nevada National Security Site (NNSS) for testing. Concurrently, a full-scale surrogate “BF3 detector”, fabricated with air replacing the BF3, was constructed for the purpose of evaluating the ability of the design to survive being dropped from a height that would be typical when performing a field replacement of an NDM on the tallest portal monitor configuration. This height corresponds to a condition such that the bottom of the NDM is at an elevation of 15 feet, or 457 cm, above ground level. This paper will discuss the design features of the detectorsystem, mitigation techniques developed to ameliorate the hazards posed by the BF3 gas, drop test results, and discussion of neutron detection efficiency for the constructed detectorsystem. BF3 detectors potentially have direct applicationsto international safeguards where 3He neutron detectors are typically deployed.