Detecting the Arrival of Air Showers

A cosmic ray primary particle—mostly highly energetic protons—is able to produce an extensive air shower in the Earth’s atmosphere, with a cascade of secondary particles. Evidence of the existence of such showers, which dates back to 1930s, comes from coincidence events involving two or more detectors placed some distance apart, which signal the simultaneous arrival of particles belonging to the shower. Although with a low yield, such evidence may also be obtained by experiments performed with small Geiger counters, as discussed in the present Section.