Study of cosmic ray composition in the knee region using multiple muon events in the Soudan 2 detector

Deep underground muon events recorded by the Soudan 2 detector, located at a depth of 2100 m of water equivalent, have been used to infer the nuclear composition of cosmic rays in the ``knee'' region of the cosmic ray energy spectrum. The observed muon multiplicity distribution favors a composition model with a substantial proton content in the energy region 8×10⁵--1.3×10⁷ GeV/nucleus.