Double ionization of helium by fast electrons: use of correlated two electron wavefunctions

The mechanism for the simultaneous escape of two equivalent electrons from a noble gas atom is strongly related to interelectronic correlation. It is therefore necessary to use correlated wavefunctions to describe the system in its initial and final states. As a first step towards the study of other noble gases, the double ionization of the helium atom by fast electrons is studied in a first Born approximation approach by applying Hylleraas-type functions for the initial state and a correlated double-continuum wavefunction which satisfies the exact asymptotic boundary conditions for the final state of the two slow electrons.