Sound velocity measurements by x-ray shadowgraph technique for melting phenomena at ultrahigh-pressure regime

Developments in measuring sound velocity of matter under ultrahigh pressure are described. We employed a time-resolved x-ray shadowgraph technique to measure the sound velocity of shock-compressed diamond and iron foils at around melt. The sound velocity significantly dropped at melting, a behavior that has been difficult to clarify by conventional measurements by subtracting particle velocity from shock velocity (u(s) - u(p)). In addition to sound velocity, other important parameters were also obtained simultaneously.