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. The effective coincidence energy resolutions and transmission functions are defined, and their importance clearly demonstrated.