IMB (for Irvine-Michigan-Brookhaven detector)
was an neutrino detector located in a mine in Ohio
operating 1981 through 1991, a Cherenkov detector
consisting of a tank of pure water surrounded by photomultiplier tubes. Among
the detectors accomplishments was detection of a neutrino burst
coincident with the EMR of SN 1987A reaching Earth.
Though it functioned as a working neutrino observatory,
its original aim was to detect proton decay within the water
tank, and finding none over the course of a year
implied a protonhalf-life on the order
of 1031 years or more.