Čerenkov Radiation from Protons and the Measurement of Proton Velocity and Kinetic Energy

High velocity protons ($\beta =0.68\mathrm{}$) from the electrically deflected external beam of the 184-in. cyclotron were sent through materials of high index of refraction (crystalline silver chloride and extra dense flint glass), and light was detected photographically with the intensity and angular distribution characteristics of Čerenkov radiation as predicted by Frank and Tamm. This is the first observation of this radiation from particles other than electrons and proves that the radiation is not a function of the mass of the particle. The heavier particle suffers less scattering and change of energy in the material and allows the highly directional character of the radiation to be observed. By removing the effects of chromatic disperion with a suitable prism, the angular intensity distribution was reduced to a bell-shaped distribution about the predicted angle with a standard deviation of around fourteen minutes of arc. This approaches the delta-function distribution derived by Frank and Tamm. The light was shown to be totally plane polarized in the direction predicted by Frank and Tamm.