  Time-resolved radiography can be used to obtain absolute shock Hugoniot
states by simultaneously measuring at least two mechanical parameters of the
shock, and this technique is particularly suitable for one-dimensional
converging shocks where a single experiment probes a range of pressures as the
converging shock strengthens. However, at sufficiently high pressures, the
shocked material becomes hot enough that the x-ray opacity falls significantly.
If the system includes a Lagrangian marker, such that the mass within the
marker is known, this additional information can be used to constrain the
opacity as well as the Hugoniot state. In the limit that the opacity changes
only on shock heating, and not significantly on subsequent isentropic
compression, the opacity of shocked material can be determined uniquely. More
generally, it is necessary to assume the form of the variation of opacity with
isentropic compression, or to introduce multiple marker layers. Alternatively,
assuming either the equation of state or the opacity, the presence of a marker
layer in such experiments enables the non-assumed property to be deduced more
accurately than from the radiographic density reconstruction alone. An example
analysis is shown for measurements of a converging shock wave in polystyrene,
at the National Ignition Facility.
