The Evolution of Neutron Straw Detector Applications in Homeland Security

The dwindling supply of ³He has necessitated the adoption of new technologies for detection of neutrons especially in Homeland Security (HS), where detectors require large volumes of the precious gas. The boron-coated straw (BCS) technology consists of very thin-walled metal tubes equipped with a highly robust coating of ¹⁰B₄C on the inner wall. The coating, applied with Physical Vapor Deposition (PVD), is atomically bound to the metal substrate, and it is able to resist delamination over a temperature range from -200^° C to 1000^° C. Accelerated lifetime testing of sealed straw detectors over extreme temperature ranges (-70^° C to +125^° C) have recently demonstrated a 99% expected lifetime of 30 years. At the same time, the coating purity is high, with a ¹⁰B content approaching 77%. Straws stacked 5 deep in a dense array have demonstrated an efficiency of > 70% when evaluated in a cold neutron beam. A number of field worthy HS detectors have been developed over the past 2 years based on the BCS. Examples are presented, including neutron modules for Radiation Portal Monitors (RPM), a vehicle mounted modular detector with an intrinsic efficiency of 30% for unmoderated ²⁵²Cf neutrons, and handheld detectors. All of these systems have been government tested. The ¹⁰B₄C coated straw offers a highly versatile, robust and low cost technology meeting multiple needs in homeland and international security.