The IMB-3 experiment was a large water Cherenkov ring imaging detector with
a fiducial mass of 3.3 kton. During a 7.6-kton-year exposure (similar to 4
.6 x 10(33) nucleon yr) 935 contained events were observed. The observed ra
te and characteristics are consistent with the expected backgrounds from at
mospheric neutrinos. Lower limits on the nucleon lifetime are set for a wid
e variety of proposed decay modes. [S0556-2821(98)00323-3].