Figure 3: Plot of lattice rotation angle against peak pressure.

The rotation angle is measured for rotation of the lattice about the [100] and [010] directions. The mean is taken for all visible diffuse peaks, with error bars corresponding to the minimum and maximum fitted rotation angles. Pressure is determined using VISAR velocity profiles and the bulk copper Hugoniot. The velocity profiles were extracted from the VISAR interferograms using the Fourier transform method described by Celliers et al.³¹ The mean velocity during the X-ray pulse is then converted to a pressure using the Hugoniot. The errors are calculated using the s.d. of the fringe shift, converting to velocity, and hence pressure, then taking the minimum and maximum values during the X-ray pulse.