Electron impact double ionization in magnesium

Experimental investigations of double ionization provide information on the mechanism by which two electrons can be simultaneously removed from an ato m. Information on the two-electron momentum distribution function of the el ectrons can also be obtained from the experiments. Results for the double i onization of magnesium are summarized and new (e,3e) data presented. Under a variety of experimental conditions evidence has been found for orientatio n and polarization effects. In addition, the recoil momentum of the residua l doubly-charged ion is often large implying large momentum transfer to the core or ionizing collisions that occur close to the nucleus.