in physics, the almost simultaneous detection of two nuclear or subatomic particles (e.g., within a time of 10⁻⁵ second). Coincidence counting involves two or more particle counters exposed to the same source of particles and connected to an electronic coincidence circuit. One use of the coincidence technique is to detect particles emitted simultaneously from the same nucleus—e.g., a beta particle and a gamma ray photon. The technique is also important in the study of cosmic rays and in experiments with subatomic particles.

In anticoincidence counting, two counters are connected so that a pulse is recorded by one of them only if there is no simultaneous pulse in the other. This is useful in rejecting particles that do not originate from the source being studied.