Coincidence circuit

In physics, a coincidence circuit is an electronic device with one output and two (or more) inputs. The output activates only when the circuit receives signals within a time window accepted as at the same time and in parallel at both inputs. Coincidence circuits are widely used in particle detectors and in other areas of science and technology.

Walther Bothe shared the Nobel Prize for Physics in 1954 "...for his discovery of the method of coincidence and the discoveries subsequently made by it." Bruno Rossi invented the electronic coincidence circuit for implementing the coincidence method.

In his Nobel Prize lecture, Bothe described how he had implemented the coincidence method in an experiment on Compton scattering in 1924. The experiment aimed to check whether Compton scattering produces a recoil electron simultaneously with the scattered gamma ray. Bothe used two point discharge counters connected to separate fibre electrometers and recorded the fibre deflections on a moving photographic film. On the film record he could discern coincident discharges with a time resolution of approximately 1 millisecond.

In 1929, Walther Bothe and Werner Kolhörster published the description of a coincidence experiment with tubular discharge counters that Hans Geiger and Wilhelm Müller had invented in 1928. The Bothe-Kohlhörster experiment showed penetrating charged particles in cosmic rays. They used the same mechanical-photographic method for recording simultaneous discharges which, in this experiment, signalled the passage of a charged cosmic ray particle through both counters and through thick wall of lead and iron that surrounded the counters. Their paper, entitled Das Wesen der Höhenstrahlung", was published in the Zeitschrift für Physik v.56, p.751 (1929).

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