What is the highest energy ever seen in a cosmic ray?
There are several events worth mentioning. In the 1960’s, a ground array of 19 detectors spread over 8 square kilometers was built at Volcano Ranch, New Mexico, by a team led by John Linsley. In 1963, his team reported an observation of a cosmic ray with an energy greater than 1020 eV. Since then, several large detector arrays have been built to search for very high energy csomic rays. One such detector, called the Fly’s Eye, and built in the Utah desert, observed a cosmic ray shower in 1991 that at it’s maximum contained 200 billion particles in the shower. The energy of the primary particle was 3 x 1020 eV, the highest energy cosmic ray ever observed. While the composition of the primary particle isn’t known with certain, the best guess is that it was a moderate mass nucleus (something like oxygen).
