Collaborative Proposals 1038700 (PI: Hongxing Jiang, Texas Tech University) 1038890 (PI: James Edgar, Kansa State University) ARI-MA: Collaborative Research: Hexagonal Boron Nitride Based Neutron Detectors
Fundamental studies on the properties and processing of hexagonal boron nitride (hBN) will be performed to enable the fabrication of nearly ideal solid state thermal neutron detectors. Epitaxial films of this wide band gap semiconductor, prepared by metalorganic chemical vapor deposition, will be intentionally doped to control its electrical and optical properties. High structural quality, bulk hBN crystals will be grown from molten metal solutions, so the impact of extended defects on its properties can be determined. The hBN materials will be prepared with isotopically-enriched boron-10, to take advantage of its high thermal neutron capture cross section to enhance detector sensitivity. Definitive values of the fundamental properties of hBN will be determined by advanced materials characterization techniques. Solid state neutron detectors, including devices employing a novel multiple layer structure that can accommodate short mean free paths of charge carriers, will be fabricated, and their neutron detection ability thoroughly tested. Ultimately, the detectors developed is expected to have a major impact on nuclear threat detection and could lead to a large variety of useful devices, ranging from small disposable detectors to large area monitors, and provide an alternative to helium-3 based detectors. Graduate and undergraduate students from both participating institutions will be actively involved in this highly interdisciplinary research project.
Not only are He-3 gas tube based neutron detector systems are bulky, hard to configure, require high voltage operation, and difficult to transport via air shipment, but there is a significant shortage of He-3 gas. The major objective of this joint program by Texas Tech University and Kansas State University is to conduct fundamental studies on the properties and processing of semiconducting hexagonal boron nitride (hBN) materials to enable the fabrication of solid state thermal neutron detectors. Epitaxial films of this wide band gap semiconductor have been prepared by metalorganic chemical vapor deposition. High structural quality, bulk hBN crystals have been grown from molten metal solutions. Micro-strip metal-semiconductor-metal detectors were fabricated from hBN epilayers and exhibited an effective conversion efficiency approaching ~80% for absorbed neutrons. Our results indicate that, by combining the neutron capture and carrier collection in the same material, hBN semiconductors would enable the development of essentially ideal solid-state thermal neutron detectors with efficiencies far exceeding the current state-of-the-art. Graduate and undergraduate students have been actively involved in this highly interdisciplinary research project. The support has resulted in one journal publication: "Hexagonal boron nitride epitaxial layers as neutron detector materials," J. Li, R. Dahal, S. Majety, J.Y. Lin, and H.X. Jiang, Nuclear Inst. and Methods in Physics Research, A (2011) doi:10.1016/j.nima.2011.07.040 .
