ABOUT SOME EXPERIMENTAL ASPECTS OF DOUBLE AND TRIPLE COINCIDENCE TECHNIQUES TO STUDY ELECTRON-IMPACT DOUBLE IONIZING PROCESSES

A critical discussion is given of some of the experimental parameters involved in measurement of the three-, four- and five-fold differential cross sections obtained in (e, 2e), (e, (3 - 1)e) and (e, 3e) experiments, respectively. Features observed in the triple coincidence time-delay spectrum are attributed to fully accidental, semi-accidental or true triple coincidence events. Formulas are given that allow computation of the true coincidence rate, the percentage statistical error and the signal-to-background ratio, and to optimize the gas density-electron beam current product for any given experiment. For the first time, to our knowledge, the effective coincidence energy resolutions and transmission functions are defined, and their importance clearly demonstrated.