Since his retirement in June, Courant's interest in high energy or particle physics hasn't subsided. He's around all the time. The first of Courant's projects in the mine, owned by the state of Minnesota, was a nucleon decay experiment.
Nucleons are the protons and neutrons of an atom.
Courant's experiment involves witnessing the rarely observed breakdown of nucleons into their component particles. The project began with the construction of a 1,000-ton particle detector located 2,300 feet underground. Courant and other members of the University's Experimental High Energy Group built it to reduce interference from the millions of subatomic particles that constantly bombard the Earth's surface. In the three and a half years that the detector has operated, the scientists have found some promising examples of nucleon decay but nothing definite. Neutrinos are neutral electron-like particles that originate from the sun or cosmic rays in space.