Paper EM-ThP8
Investigating U₃O₈ for Solid-State Direct-Conversion Neutron Detection Applications

Thursday, November 10, 2016, 6:00 pm, Room Hall D

Solid-state direct-conversion neutron detectors, wherein a semiconductor detector heterostructure is made up of a neutron absorbing material, are capable in principle of very high neutron detection efficiencies. High-efficiency direct-conversion detectors have not yet been achieved in practice, however, because of challenges in finding suitable materials that simultaneously meet the necessary criteria, including high neutron absorption, high mobility–lifetime product, and low leakage current. Uranium-oxide-based semiconductors make up a promising class of neutron detection materials as uranium undergoes neutron-induced fission to yield very high energy primary reaction products, which can in turn create a large number of electron–hole pairs—two-to-four orders of magnitude higher than in the case of boron and lithium, the materials commonly studied for direct-conversion detectors. This additional charge can help to overcome limitations in charge transport properties, such as high leakage current and low charge carrier mobility, typically seen in candidate neutron-absorbing semiconductor materials. Of the uranium oxides, UO₂ has been studied the most, and literature reports show that its resistivity and charge carrier mobility vary widely with stoichiometry and microstructure. Very few studies on the electrical transport properties of U₃O₈ exist, with one reporting values of 10⁴ Ω cm for resistivity and 1 cm²/ V s for mobility (George & Karkhanavala, 1963). Like for UO₂ and other semiconductors, however, these properties would be expected to vary widely. To determine the range of the possible charge transport properties in U₃O₈, as well as how they vary with material composition and microstructure, a rigorous study is necessary. We report the results of charge transport measurements using a range of techniques, including four-point van der Pauw resistivity and DC Hall, on sintered U₃O₈ pellets of varying stoichiometry and grain size. Additionally, we report results from ultraviolet and x-ray photoelectron spectroscopy toward probing the electronic structure of the U₃O₈ surface toward the development of suitable electrical contacts for this material.

George, A. M., & Karkhanavala, M. D. (1963). Studies on the electrical properties of uranium oxides I. Electrical conductivity of alpha U3O8. J. Phys. Chem. Solids, 24, 1207–1212. doi:10.1103/PhysRevB.81.205324