Ultrahigh-pressure shock-wave experiments

The author has obtained Hugoniot data for uranium at a pressure of 6.7 TPa using a planar shock generated by an underground nuclear explosion. Measurements were made relative to a molybdenum standard in an impedance-matching experiment using 200-mm-diam by 20-mm-thick samples of each material. Twenty-seven electrical contact pins were used to measure shock velocities of 27.0 and 22.8 km/s (±{}1%) in the molybdenum and uranium, respectively; these velocities correspond to pressures and densities of 4.97 TPa and 30.8 g cm^-3 (Mo) and 6.69 TPa and 59.0 g cm^-3 (U). The measurement differs from a theoretical calculation by more than 2.5 times the experimental uncertainty and represents the highest pressure at which Hugoniot data have been obtained.