REEXAMINATION OF COSMIC-RAY COMPOSITION AROUND 10(18) EV FROM FLYS EYE DATA

The cosmic-ray composition around 10(18) eV is reexamined using the Ch ou-Yang model for the simulation of air showers and comparing with Fly 's Eye data. This model is quite different from models previously used . Using this model leads to the same conclusion that the primary cosmi c-ray composition gets lighter in the region from 3 x 10(17) eV to 10( 19) eV. This conclusion of a changing composition is not sensitive to the choice of model because it results from the measured elongation ra te being greater than that predicted for a constant composition by any reasonable model that can account for the measured depths of shower m axima at the Fly's Eye threshold energy. That constraint on elongation rate for a constant composition also implies that the increased rate of energy dissipation that appears in hadron-nucleus interactions near 10(14) eV may continue up to the region of 10(19) eV.