No abstract

No abstract

We report a direct measurement of temperature in a shocked metal using Doppler broadening of neutron resonances. The 21.1-eV resonance in 182 W was used to measure the temperature in molybdenum shocked to 63 GPa. An explosively launched aluminum flyer produced a planar shock in a molybdenum target that contained a 1-mm thick layer doped with 1:7 at: % 182 W. A single neutron pulse, containing resonant neutrons of less than 1 s duration, probed the shocked material. Fits to the neutron time-of-flight data were used to determine the temperature of the shocked molybdenum.

The principal Hugoniot of molybdenum has been determined at a pressure of 2.0 TPa by measuring directly both the shock velocity and the particle velocity behind the shock. Neutrons from an underground nuclear explosion were used to generate a high-pressure shock in a slab of molybdenum by rapidly fission heating an adjacent slab of enriched uranium. A shock velocity of 18.2 mm/μs (±5%) was obtained by determining the transit time of the planar shock between two points in the molybdenum separated by 9.87 mm. A particle velocity of 10.7 mm/μs (±5%) was obtained by observing the Doppler shifts of six neutron resonances in the energy region from 200 to 800 eV in the moving shocked molybdenum. The pressure and density derived from this pair of measurements are 2.0 TPa (20 Mbar) and 24.8 g cm−3, respectively. This experiment represents the first direct determination of a point on the Hugoniot of any material in this pressure region, and the resulting data point is in good agreement with theoretical estimates. This measurement was a successful demonstration that the Doppler-shift technique can be used to obtain particle velocities in this pressure region. It appears that errors in both the shock velocity and the particle velocity can be reduced to approximately ±2% in an improved measurement, resulting in a well-defined Hugoniot for molybdenum, which can be used as a standard in future impedance-matching 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 gcm (Mo) and 6.69 Tpa and 59.0 gcm (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.