Proton radiography with high energy protons is a new technique being
developed to ``look'' inside dense objects.  A high energy beam
illuminates the object.  Protons undergo elastic collisions or inelastic
collisions within the object depending on the material which is
traversed (dependent on density, atomic number, atomic weight, reaction
cross sections, etc.).  The inelastic collisions which result in the
loss of the proton are responsible for attenuating the incident beam.
Inelastic collisions such as ionization energy loss and multiple coulomb
scattering ($\delta$-ray production) change the energy and the direction
of the protons, but do not attenuate them out of the beam.
The scattered beam of exiting protons is then focussed through a
quadrupole lens system to an image on a detector array.

The utility of protons for radiography is related to the relatively low
attenuation through thick objects, the small backgrounds on the image
plane and the ability to provide multiple axes and multiple time pulses
along the axes.  These last two features will allow a three dimensional
"movie" to be made of complex, shocked metal systems in experiments
refered to as hydrotests.