  Proton radiography is used in various high-energy-density (HED) plasma
experiments. In this paper, we describe a Monte Carlo and ray-tracing
simulation tool called MPRAD that can be used for modeling the deflection of
proton beams in arbitrary three dimensional electromagnetic fields, as well as
the diffusion of the proton beams by Coulomb scattering and stopping power. The
Coulomb scattering and stopping power models in cold matter and fully ionized
plasma are combined using interpolation. We discuss the application of MPRAD in
a few setups relevant to HED plasma experiments where the plasma density can
play a role in diffusing the proton beams and affecting the prediction and
interpretation of the proton images. It is shown how the diffusion due to
plasma density can affect the resolution and dynamical range of the proton
radiography.
