Boron Coated Straw Detectors as a Replacement for 3He

The disappearing inventory and minute natural abundance of He-3 gas necessitate the adoption of new technologies for the detection of neutrons. The exclusive source of He-3 on Earth is derived from the tritium stockpile, which decays to He-3 at a rate of 5.5% per year. Despite the low He-3 supply, and uncertain production rate in the future, this medium remains by far the most attractive for many applications. The DHS and DOD plan to equip major ports of entry with large area monitors, in an effort to intercept the smuggling of nuclear materials. The desired world deployment of such monitors alone could consume the entire He-3 supply, limiting the prospects of nuclear science and other applications that rely very heavily on He-3-based detectors as well. Clearly, alternate neutron detection technologies must be developed. We propose a technology based on close-packed arrays of long aluminum or copper tubes (straws), 4 mm in diameter, coated on the inside with a thin layer of B-10-enriched boron carbide ((B4C)-B-10). A close-packed array of straw detectors offers a stopping power for neutrons equivalent to that of 2.68 atm of He-3 gas. In addition to the high abundance of boron on Earth and low cost of B-10 enrichment, the boroncoated straw (BCS) detector offers distinct advantages over conventional He-3-based detectors, including faster signals, short recovery time (ion drift), low weight, safety for portable use (no pressurization), and low production cost. The above are all critical for large detector deployments, as in portal monitoring, and for active interrogation applications, where fast signals can significantly improve performance. Furthermore, in imaging applications, the BCS high level of segmentation supports high count rates and parallax-free position encoding, both difficult to achieve in conventional He-3 pressure vessels. We review the use of the BCS detector in a variety of applications, pointing out its distinct advantages over conventional He-3 tubes.