Combined Effect of Ultrahigh Pressure and Nuclear Irradiation on Solid—Solid Phase Transformations

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Abstract
A special Bridgman opposed diamond anvil apparatus was constructed to generate useful static pressures up to 50 kbar at ambient temperatures. It was designed to function in the environment of a nuclear reactor to thermal fluxes of 1018 nvt. The bulk of the study deals with ZrO2; other materials investigated to varying degrees were PbO2, BN, B2O3, B, silicic acid, SiO2, BaTiO3, graphite, P, Ni, Zr, and U. The samples were exposed while under pressure to fast neutron fluxes (>2.8 MeV) of 4.1×1015 nvt. The boron‐containing samples suffered up to 2×1018 fissions/cc while under pressure. PbO2, BN, B2O3, silicic acid, graphite, SiO2, and Zr were bombarded by uranium fission fragments to 6.5×1011/cm2. ZrO2 was bombarded with 2×1016 nvt epithermal neutrons and 1.6×1014 fission fragments/cm2. There was no evidence of any irradiation‐pressure‐promoted phase change. Pressure alone converted tetragonal ZrO2 to the monoclinic form and cubic ZrO2 transformed to tetragonal plus monoclinic phases. A PbO2 rutile → orthorhombic transformation occurred in seconds at room temperature along with a pressure‐sensitive optical absorption edge above 20 kbar.

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