Fluctuations in the Energy Loss of 66- and 100-MeV Protons in a Thin Proportional Counter

Fluctuations in the energy loss have been measured for 66- and 100-MeV protons passing through a proportional counter filled with 11.0 mg/${\mathrm{cm}}^2$ of a gas mixture of 90% xenon plus 10% methane. The measured values are consistent with the theoretical values determined from the Vavilov theory for energy-loss fluctuations; however, when the Vavilov theory is corrected for the binding effect of the electrons based on the formulation of Shulek et al., the corrected theoretical energy-loss distributions do not agree with the experimental distributions.