Proton Stopping Power of Solid Beryllium

The energy loss of protons penetrating beryllium foils of different thicknesses has been determined as a function of the proton energy by measuring the shift of those potentials at which a thin aluminum target gives resonance radiation. The experimental points fit within ±{}2 percent a theoretical curve corresponding to an average ionization energy of 64±{}5 ev, which is in agreement with a recent theory for the stopping power of metals.