Replacement of 3He in constrained-volume homeland security detectors

We have developed a boron-coated straw (BCS) detector to replace a ³He-based design for homeland security. BCS detectors are distributed inside a high-density polyethylene (HDPE) moderator, occupying the exact same volume of the ³He-based design. The design challenge was to achieve similar neutron detection efficiency as the ³He design, without increasing the overall size and weight of the assembly, while at the same time providing robust operation in the field. Prototype detectors of this design were built and tested with a ²⁵²Cf source. The ³He-based detector was also tested under identical conditions for comparison. Results show that the BCS-based design has comparable response to the ³He detector, and can thus be an attractive replacement detector. The high detection efficiency of the proposed design is partly due to the small diameter of the BCS, which allows for the detection medium (¹⁰B) to be efficiently dispersed throughout the moderator, dramatically increasing the probability that neutrons are captured in the detector, rather than escape, or be absorbed in the moderator itself. As a result, the BCS using distributed moderation can perform very well in sensitivity comparisons with ³He gas where other technologies fall short. At the same time, the BCS offers distinct additional advantages over conventional ³He-based detectors, and alternate technologies such as ¹⁰BF₃ tubes and ¹⁰B-coated rigid tubes. These include many-times faster electronic signals, no pressurization, improved gamma-ray rejection, no toxic or flammable gases, easy maintenance, and effective field use compatibility.