Multiple detector triple coincidence spectrometer for (e,3e) electron impact double‐ionization measurements

An (e,3e) spectrometer for the study of double ionization of magnesium by electron impact is described. With the spectrometer the angular and energy distributions of the ejected electrons can be measured over a range of incident‐electron energies. The spectrometer incorporates two ejected‐electron electrostatic energy analyzers and a tandem electrostatic analyzer for the scattered electrons. Up to eight detectors can be placed at the focal planes of each of the ejected analyzers. This increases the data rate by a factor of 64 over arrangements with two ejected‐electron detectors. In order to reduce noise and establish the energy of the final state of the doubly charged residual magnesium ion, triple‐coincidence electronics are used with a preprocessing circuit to reduce dead time. The first double‐ionization study with the instrument was the ejection of a 2p inner valence electron by a 3.5 keV incident electron accompanied by the subsequent filling of the 2p hole and the emission of a 35 eV Auger electron.