Results from the Soudan 1 detector

We have searched for the spontaneous decay of protons and bound neutrons using Soudan 1, a 31.5-metric-ton iron-loaded concrete tracking calorimeter, instrumented with 3456 proportional tubes. During a live time of 0.382 years, we have observed one candidate event wholly contained within the detector. If we attribute this event to a background source, we can establish a lower bound (90 percent confidence level) on the lifetime for nucleon decay through any of a wide range of modes of 1.0 x 1030 years. The Soudan 1 nucleon decay detector is also capable of identifying slowly moving single particles which traverse the detector if they have velocities between 0.001c and 0.01c, and ionize at least half as much as a relativistic muon. Magnetic monopoles predicted by grand unified theories may satisfy these conditions. During a live time of 0.39 yr, no candidate has been observed implying a 90-percent confidence-level limit on the flux of such objects of less than 4.1 x 10-13/(cm2 sr sec) over the velocity range above. Results from a study of multiple-muon events are also discussed. The Soudan 1 detector began operation in May 1981, and has produced reliable data since October 1981. We present here preliminary results from three classes of data that have been obtained, on nucleon decay, magnetic monopoles and multiple-muon events