Equation of State Measurements at Low Pressure in Tin Using of 800 MeV Proton Radiography

A 2cm long 8 mm diameter cylindrical tin target has been shocked to a pressure in the region of the $\beta \diamondsuit \gamma $ phase change using a small, low density PETN charge mounted on the opposite side of a stainless steel diaphragm. The density jump and shock velocity were measured radiographically as the shock wave moved though the sample and the pressure dropped, using the proton radiography facility at LANL. This provided a quasi-continuous record of the equations of state along the Hugoniot for the P1 wave from a shock velocity of 3.25 km/sec down to near the sound speed. Edge release effects were removed from the data using tomographic techniques. The data show evidence for a phase transition that extends over a broad pressure range. The data and analysis will be presented.