Single and double electron removal from helium by protons

The independent event model (IEV) is used to calculate single and double electron removal cross sections for p+ + He collisions. The single electron removal cross sections are in good agreement with experiment. In contrast to the model of Janev and co-workers, it is found that the single electron removal cross section for p+ + He+ is much larger than the double electron removal cross section for p+ + He, since in small impact parameter collisions of protons with He the probability of removing the first electron is less than unity. Double electron removal cross sections for p+ + He calculated in the IEV are found to be in poor agreement with experiment, in contrast to p-+ He where good agreement was obtained. (author)