1962

Linsley detects first 10²⁰ eV cosmic ray

In the late 1950s, American physicist John Linsley worked with Livio Scarsi from the University of Milan to build an array of nineteen plastic scintillation detectors at Volcano Ranch near Albuquerque, New Mexico. On February 22, 1962, using these ground-based detectors, Linsley identified the first cosmic ray with an energy higher than 10²⁰ eV—the highest energy cosmic ray particle ever detected at the time. Their observations suggested that not all cosmic rays are confined to the galaxy, clarified the structure of air showers, and provided the first evidence of ultra-high-energy cosmic ray composition and arrival directions.