Dips and backward peaks in the helium (e,2e) differential cross section atlow energies

Two investigations have been carried out of the helium (e,2e) process. The first concerns the sharp dip that exists at ari incident electron energy of 64.6eV and for equal energies and angles of the two outgoing electrons. Th e sensitivity of this dip to the asymmetry of the angles of the outgoing el ectrons has been measured and it has been found that the dip exists over a wide range of asymmetric angles, but with an almost constant angle between the two electrons. In the second investigation a new 'magnetic angle-changi ng' technique has been used to observe the two outgoing electrons when one of them moves in the same direction as the incident electron and the other moves in the opposite direction, and a peak has been found in the triple di fferential cross section when the incident electron energy is 40eV and outg oing energies are 4 and 11eV.