Double ionization of He by electron impact at large momentum transfer

The double ionization of He by electron impact at 580 eV has been studied in a coplanar symmetric (e,(3-1)e) experiment, in which two fast electrons of 250 eV are detected. In this way a momentum transfer as large as 6 a.u. is achieved. The results are compared with the predictions of a theoretical model based on the impulse (knock-out) approximation. The calculations, which include radial correlation of electrons in the He ground state wave function, better describe the experiment than those with an uncorrelated wave function.