Electron ejection by positron impact ionization

The ejected-electron energy spectrum resulting from positron impact ionization of molecular hydrogen has recently been measured at an incident energy of 50 eV. The ejected electron and the scattered positron have been measured in coincidence around 0 deg. with a new parallel-plate analyser having time-focusing properties. A 1.6 eV shift towards lower energies has been found in the electron-spectrum relative to a theoretical prediction. The shift may indicate the occurrence of ionization simultaneous to another energy loss, e.g. vibrational excitation or molecular dissociation of the target. To test this hypothesis, studies have begun with a helium target