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.

A man wearing rainbow suspenders leaning against a yellow car in a desert landscape.
This photo of John Linsley is from the Fermilab History and Archives Project. It was taken in 1977 and most likely depicts Linsley near the Volcano Ranch experiment in New Mexico, where Linsley observed the first ultra-high-energy cosmic ray.