Structures in the cross section of double ionisation of helium by the impact of fast charged particles

Abstract
In this work the five-fold differential double-ionisation cross section of helium by the impact of fast charged particles has been investigated. The case is considered in which little momentum is transferred to the target so that a Born-type approximation in the projectile-target potential can be employed. A scaling formula for the cross section has been derived which relates cross sections resulting from the impact of projectiles of different masses and charges. Further, collision geometries have been found for which maxima and minima arise in the cross section and the associated ionisation mechanisms have been identified. Necessary kinematical conditions for the Bethe ridge in double ionisation have been worked out.