B-Lined Proportional Counters to Traditional Neutron Counting Applications in International Safeguards

Many neutron-detection techniques are under consideration as potential replacements for 3 He gas-filled proportional tubes, which are widely used in international nuclear safeguards applications. The traditional 10 B-lined proportional tube is a commercial off-the-shelf (COTS) technology for neutron detection that predates the development of 3 He detectors. There is also a long history of its use in neutron counting facilities and in modeling, design, and testing of assay systems. When compared to the familiar 3 He tube, cylindrical 10 B-lined proportional counters meet or exceed all relevant criteria (e.g., stability, resistance to gamma-ray exposure) with the exception of neutrondetection efficiency per unit volume. The thin boron coating thickness and practical active detection area per unit volume limit the measurement performance ultimately achievable with these detectors; however, assay systems based on the 10 B-lined proportional detector can be constructed with sufficient measurement performance to achieve the International Target Values [1] for a significant subset of traditional safeguards neutron counting applications. Additionally, these detectors are also well suited to a number of active neutron interrogation applications such as the differential die-away and 252 Cf shuffler techniques, which can be accomplished with lower detection efficiency than when using the detectors’ passive counterparts. As part of our studies of alternative 3 He technologies, we examined the performance of a set of commercially manufactured neutron-slab-counting assemblies configured as a neutron coincidence collar, a passive neutron coincidence well counter, and the detector assembly within a large-cavity 252 Cf shuffler. Measurement performances are presented and compared with those of the standard 3 He-based counting counterparts. These performance levels represent a baseline of what can be achieved using COTS neutron counting systems with no significant development required. They are a minimum baseline against which the anticipated performance of any other potential alternative technology, and the associated portion of the safeguards application space it could address, can be judged.