Electronic anticoincidence

Early experimenters in X-ray and gamma-ray astronomy found that their detectors, flown on balloons or sounding rockets, were corrupted by the large fluxes of high-energy photon and cosmic-ray charged-particle events.

Gamma-rays, in particular, could be collimated by surrounding the detectors with heavy shielding materials made of lead or other such elements, but it was quickly discovered that the high fluxes of very penetrating high-energy radiation present in the near-space environment created showers of secondary particles that could not be stopped by reasonable shielding masses.

[2] Plastic scintillators are often used to reject charged particles, while thicker CsI, bismuth germanate ("BGO"), or other active shielding materials are used to detect and veto gamma-ray events of non-cosmic origin.

A plastic scintillator may be used across the front which is reasonably transparent to gamma rays, but efficiently rejects the high fluxes of cosmic-ray protons present in space.

[3] Modern experiments in nuclear and high-energy particle physics almost invariably use fast anticoincidence circuits to veto unwanted events.