The use of high-energy protons (20–50 GeV) to probe the internal structure of thick objects has added a new dimension to radiographic studies. One may mention [1], among other studies: 1. The mean free path λ of high-energy protons is much longer than that of x-rays. The huge difference in the mean free paths has an important consequence. For example, the beam attenuation factor (N 0 /N) of high-energy protons in C, Fe, Pb with a thickness 200 g/cm 2 are 28, 11, and 6, respectively, while those of 15-MeV x-rays are 30, 518, and 66910. In other words, high-energy protons penetrate much deeper into materials. 2. The proton is a charged particle. It, therefore, interacts with material through both the electromagnetic and strong nuclear interactions, thus providing valuable information on the material compositions, such as the ratio Z/A, of the targets.