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There is significant interest in developing efficient, direct conversion, neutron sensitive solid-state radiation detector materials with the ability to discriminate between photon and neutron events. Recently, this has led several research groups to pursue uranium dioxide (UO2) single crystals as a detection material due to the large reaction energy (~185 MeV) from a neutron induced fission event. The resulting electrical pulse, generated primarily by the energetic fission fragments, is expected to be on the order of 165 MeV, which is much greater than current detection schemes which rely on reaction energies between 2-6 MeV. The primary technical challenge to the successful fabrication of UO2 devices is the lack of high quality (semiconductor grade) single crystals of UO2. The high melting point of UO2 (~2878°C) precludes the use of traditional melt growth techniques like Czochralski. While exotic melt growth techniques such as arc fusion, cold crucible, and solar furnace have successfully grown UO2, the crystal quality suffers from both thermal strain and oxygen non-stoichiometry, two particularly difficult challenges inherent to uranium oxide materials.
Crystal growth of UO2 by the hydrothermal synthesis technique has never been investigated, although the method has been successfully applied to the synthesis of other refractory oxides. In this talk, we will present growth of UO2 single crystals from a variety of hydrothermal solutions at temperatures below 650C. X-ray diffraction confirmed the stoichiometric nature of the samples and X-ray photoelectron spectroscopy determined the photoelectric work function of two crystal orientations. Preliminary proof-of-concept irradiation studies of a simple UO2 resistive detector will also be presented.
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