The investigation of electron impact ionization by the electron-electron (e, 2e) coincidence technique has until recently been restricted to the non-relativistic energy region (typically 10 eV to 10 keV). We report here on an (e,2e) experiment using a 500 keV electron beam impinging upon thin-foil targets. Absolute triply differential cmss sectiom and angular distributions for K-shell ionization of silver and gold were measured, showing appreciable discrepancis compared with theoretical predictions.

Abstract. We report here on an (e, 2e) experiment at relativistic electron energies (Eo = 300 keV and 500 keV) in coplanar symmetric geometry. Absolute triple differential cross section measurements for K-shell ionisation of gold, silver and copper are compared with a number of simple first order approximations. Appreciable discrepancies between theory and experiment are found, which reduce with decreasing Z and increasing primary energy. The theoretical calculations show that spin flip effects are important in symmetric geometry, in earlier works these had been neglected.

A new high-energy (500 keV) electron–electron coincidence apparatus is described making possible for the first time triply differential cross-section measurements of inner-shell ionization of atoms of a high atomic number. Moreover, the apparatus has also been designed to deliver doubly differential ionization cross sections of the individual shells by using electron–x-ray coincidences as well as noncoincident low background spectra of inelastically scattered electrons. A special feature of the apparatus is the use of electron spectrum analyzers consisting of a nondispersive magnet and a surface barrier detector. Magnetic electron spectrum analyzers consisting of a sector field magnet and a scintillation detector have been built up. Selected measurements on tantalum (Z=73), silver (Z=47), and aluminum (Z=13) target foils are presented.

The absolute doubly differential cross section for K-shell ionisation of silver for 500 keV electron impact was measured as a function of the energy of the outgoing electrons at scattering angles of 30', 50' and 120'. Coincidences between K X-rays and outgoing electrons were used to isolate the K ionisation process for backscattering. Additionally, noncoincidence measurements of inelastically scattered electrons were made. The results are compared with theories of Cooper and Kolbenstvedt (1972), of DAS (1972), of Bell (1989) and of Elwert and Haug (1969).

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