Proton decay experiment to determine the ultimate stability of matter. A technician checking Perspex plates at the IMB Proton Decay Experiment site. The IMB Project is named after the sponsoring institutions, University of California at Irvine, University of Michigan and the Brookhaven National Laboratory. The experiment consists of a 60-foot deep tank filled with 8,000 tons of purified water, dug into the Morton-Thiokol salt mine at Painesville, Ohio, some 2,000 feet underground. The proton decay event will be detected by an array of 2,048 photomultipliers that line the tank. Proton decay is essential in most Grand Unified Theories of the fundamental forces, but to date no firm evidence of the decay has been found.