Nucleus-nucleus collisions and interpretation of cosmic-ray cascades above 100 TeV

We use low-energy data on pion production in collisions between nuclei to study some characteristics of high-energy cosmic-ray showers. The fact that pion production is suppressed in collisions initiated by heavy nuclei has the result that fluctuations in showers generated by such nuclei are larger than would be expected in some previously used models, though not so large as to impair use of air showers for studies of composition and cross section. We emphasize here implications for new cosmic-ray experiments around ${10}^9$ GeV.