Elemental composition of cosmic rays near the knee by multiparameter measurements of air showers

The small change in the spectral slope of the overall intensity of cosmic r ays near 1 PeV may be associated with the endpoint energy of supernova shoc k acceleration. A crucial test of this connection and other ideas of the or igin of the spectral 'knee' is the reliable determination of the variation of elemental composition in this region. Recent measurements at the DICE/CA SA/MIA air shower installation in Dugway, Utah, USA have provided several i ndependent air shower parameters for each event. The derivation of elementa l composition from a combination of Cherenkov size, depth of shower maximum in the atmosphere, muon size and electron size at ground level and the rel iability of these results are discussed. There is no evidence from these da ta for a large change in the mean mass of cosmic rays across the 'knee'. Th ese measurements show the cosmic rays are composed of similar to 70% proton s and a particles near total energies of 10 PeV. (C) 2000 Elsevier Science B.V. All rights reserved.