The Soudan 2 detector was used to research proton decay, atmospheric neutrino oscillations, high energy cosmic ray muons, and astrophysical point sources of cosmic rays. It was located at the same underground level as the MINOS far detector is now, half a mile deep in an abandoned iron mine in the Soudan MN State Park.
My thesis research was devoted to understanding the composition of cosmic rays at very high energies, as determined by cosmic ray muons measured in the Soudan 2 detector. My Ph.D. thesis was entitled: A Study of Cosmic Ray Composition in the Knee Region using Multiple Muon Events in the Soudan 2 Detector. A postscript version can be found here .
Post thesis, I wrote the Monte Carlo simulation of the veto shield surrounding the Soudan 2 main detector. This work was documented on its own web page located here .