Lab History: Soudan 2 Experiment

Soudan 2 Detector located in Soudan Mine Lab

The Soudan 2 detector (pictured left) was built in 1986 to attempt to observe proton decay and was tuned to observe other particle activities. Scientists were motivated to search for proton decay because certain proposed Grand Unified Theories of Physics postulated that a proton could decay or break into other particles. Additionally neutrons, the proton's neutral cousin, had been previously observed to decay. It was expected that proton decay would be analogous. While Soudan 2 never observed a decaying proton, as a result of the data gathered scientists were able to place a lower limit on a proton’s half life. That is they discovered the minimum amount of time required for a proton to begin to break into smaller particles, a proton’s half life, is at least 6x10^32 years, that’s 6 followed by 32 zeros!