Cross sections for electron-impact double ionization of magnesium have been measured in a triple coincidence experiment. When the momentum transfer is large, the double-ionization cross section as a function of the angle of the motion of the center of mass of the two ejected electrons closely resembles the analogous variation of the single-ionization cross section when the electron is ejected in a quasielastic binary collision. Assuming that the similarity in the shape of the cross section implies a similarity in the high-momentum-transfer ionization mechanism, atomic two-electron momentum densities have been derived from the data. Two-electron densities provide information on electron correlation in the atom.

• Received 10 February 1999

DOI:https://doi.org/10.1103/PhysRevLett.83.1574