The composition of cosmic rays in the knee region of the spectrum using the underground Soudan2 detector and a surface air shower array

This experiment measures the nuclear composition of cosmic rays using coincidences between the underground Soudan2 detector and a small air shower array on the surface. The surface array was operated from March 1999 until August 2000 and this analysis is based on 4600 coincident events from that time. The data suggest a composition that is a mixture of heavy and light elements in the energy region around the knee in the spectrum---between 1014 and 1016 eV/nucleus.