Range and Ionization Measurements on High Speed Protons

Abstract

The relative specific ionization along an initially mono-energetic 4-Mev proton beam has been measured. The stopping power of aluminum relative to air is found to be 1.48 mg/${\mathrm{cm}}^2$ per cm of air at 15°C and 76 cm Hg, and is also found to be independent of the energy in the interval from 1.5 Mev to 4.0 Mev. That this should be so is adequately explained in the interpretation by J. A. Wheeler. The stopping power of a variety of metal foils was also measured and the results are given. From the above measurements it is possible to calculate $I$, the mean excitation energy of atoms with many electrons (a constant which enters in Bethe's formula for the rate of loss of energy of heavy particles due to ionization) to be 0.85 $Z\left(\frac{m{e}^4}{2\hslash }\right)$ or $11.5 Z$ in electron volts.