Double ionization of he by fast protons at large energy transfer

The ratio R\(ΔE\) of double to single ionization of He by fast proton impact has been measured as a function of energy transfer \(ΔE\). While R\(ΔE\) is observed to be nearly independent of proton energy (1-6 MeV) within experimental error, it decreases with increasing energy transfer, from 2% at ΔE = 1 keV to below 1% at ΔE = 10 keV. Further comparisons of these ratios with those obtained from photoionzation and Compton scattering are made.