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 $(\sim 4.6\times {10}^{33}\mathrm{nucleon}\mathrm{}\mathrm{yr})$ 935 contained events were observed. The observed rate and characteristics are consistent with the expected backgrounds from atmospheric neutrinos. Lower limits on the nucleon lifetime are set for a wide variety of proposed decay modes.

• Received 29 May 1997

DOI:https://doi.org/10.1103/PhysRevD.59.052004