Abstract

In atomic collisions, the products that are observed following a reaction are photons, electrons, and ions. In addition to simply recording the number of events, the energy and angular distributions of the emitted photons or particles are often of interest. Although much can be learned from spectral distributions (energy or angle), frequently it is necessary to obtain more detailed information by isolating and identifying specific outcomes of a collision reaction. Such detailed information can be gained through the use of coincidence techniques, in which two or more reaction products from the same collision event are associated (or correlated) in time (see, e.g., [1–5]). This association is accomplished by electronically recording the time difference ?t between detection of the products of interest and necessarily assumes that the detected reaction products resulted from a single event. It is noted that if the detection rate for one or both of the individual reaction products is very high, then accidental coincidences from two or more separate collision events occur. To the extent that most of the recorded coincidences are due to single-collision events, coincidence techniques provide a powerful tool that permits detailed insights into collision reactions and consequently are widely used in all areas of atomic collision physics.