Oscillator strengths for double ionization in the outer shells of He, Ne and Ar

The ratio of generalized oscillator strengths for single and double ionization of He, Ne and Ar has been remeasured in the energy-loss range from threshold up to 200 eV, using 8 keV electron impact and time-of-flight ion analysis in coincidence with electrons scattered through zero degrees. The results are in excellent agreement with the recent photoionization (synchrotron) data of Schmidt et al. (1976) and appear to remove the discrepancy which previously existed between photon and electron impact work.