Bothe’s coincidence method records an event only when two or more detectors produce a signal within a very short time window. This greatly reduces background noise and allows study of correlations in radiation emitted during nuclear reactions. Using the method he probed Compton scattering and cosmic rays, providing key data that demonstrated the wave–particle duality of light and matter. Modern PET scanners and trigger systems in high-energy physics experiments are extensions of this principle. The technique is widely applied in cancer diagnosis, material inspection, and radiation therapy.

Bothe combined two or more Geiger–Müller counters and required that signals occur within tens of nanoseconds, performing strict coincidence counting. This eliminated random single-counter pulses and provided high selectivity for truly correlated particle pairs or chain reactions. With this apparatus he measured the angular distribution of the Compton effect, showing that the scattered photon and electron originate simultaneously. He also proved that cosmic rays consist of individual high-energy particles rather than a continuous radiation, paving the way for later particle physics. Coincidence techniques were later applied to plastic scintillators and semiconductor detectors, expanding into pile-up rejection, time-resolved spectroscopy, and back-to-back γ-ray studies.

Bothe’s circuitry shaped the Geiger counter pulses down to a few microseconds and used vacuum-tube logic (OR/AND) to build electronic coincidences. He implemented two-fold and three-fold coincidences, analyzing the accidental rate \(R_{acc}\approx R_{1}R_{2}\tau\) to optimise S/N theoretically. This allowed him to verify energy-momentum conservation in Compton scattering, strengthening the light-quantum hypothesis. Balloon experiments up to ~15 km measured the depth dependence of cosmic-ray intensity, suggesting that primary cosmic rays are mainly protons. His logic design is considered a precursor of modern NIM/CAMAC trigger modules and FPGA-based time-correlation measurements.