Fabrication and materials for a long range neutron-gamma monitor using straw detectors

We have previously introduced the development of a large panel monitor that can be used in the detection and localization of remote, hidden nuclear materials. The monitor employs a lightweight array of specially designed detectors that are sensitive to both neutron and gamma radiation, are safe to operate in the field, and can be manufactured in large quantities, as required for remote sensing of weak sources. The detectors are straw-like copper tubes, each 4 mm in diameter and 1 m in length, and lined with a very thin (1–2 μm) coating of enriched boron carbide (10B4C). Gammas are converted in Cu, while neutrons are converted in 10B. The feasibility of the detection method has been demonstrated previously, along with a unique application, whereby a 100×100×1.8 cm3 panel is rotated around its vertical axis. The signals generated by the rotating monitor are processed by an algorithm that can effectively identify the characteristic signature of a point source, within an unknown but uniform background. The proposed operating mode presents several challenges in fabrication, materials and packaging, including the precise and uniform coating of copper film with expensive, 10B-enriched boron carbide; use of high purity materials for the minimization of background radiation; the fabrication of an effective but lightweight neutron collimator and shield; and the fabrication of lightweight detector packaging that provides a hermetic seal, and is robust enough for portable operation in the field. We present the development of fabrication methods and some initial results.