(E,2E) COLLISIONS AT INTERMEDIATE ENERGIES

Recent experimental results will be reviewed for the atomic (e,2e) ion isation process al incident energies in the 'low energy' region, from a few eV to about 100 eV above threshold. This region is particularly interesting because it embodies all the possible complexities that can be present in the electron-impact ionisation process, such as distort ions, multiple scattering, correlations, post-collisional interactions and exchange effects. The helium (e,2e) experimental results presente d recently by the Manchester group have been obtained over an exceptio nally wide range of scattering angles, and have provided the first opp ortunity to derive multipole angular correlation information in a dire ct way. This type of analysis has been applied to measurements symmetr ic in both scattering angle and outgoing electron energy obtained at i ncident energies from 10 to 50 eV above threshold. A significant resul t is that the lower incident energies give rise to the highest multipo le components. This is a clear and direct indication that the profound effects known to be produced by electron-electron interaction in the threshold region continue to exist in the low energy region.