DOUBLE IONIZATION OF HELIUM BY ALPHA-PARTICLE IMPACT

We present cross sections for double ionization of helium by alpha-particle impact within the independent-event model. Within this model the probability of ionizing the first electron (P1) from neutral helium is calculated in the continuum distorted-wave (CDW) approximation using an explicitly correlated wavefunction of Pluvinage, whereas the probability of ionizing the second electron (P2) from the He+ ion is calculated in the CDW approximation with an eikonal initial state (CDW-EIS). The total probability for double ionization is then P1P2 rather than the P1(2) which is usually assumed in the independent-electron model. The calculated cross sections in the present model show excellent agreement with the measurement of Shah and Gilbody, at all energies above 200 keV/amu.