Charge Spectrum, Mean Free Paths, and Flux of Heavy Primary Cosmic Rays at the Top of the Atmosphere

Abstract
This investigation is restricted to primary cosmic rays of nuclear charges equal to or greater than ten at the geomagnetic latitude of 41 degrees north. Data were obtained from thick emulsions exposed at high altitudes over Texas. The flux, extrapolated to the top of the atmosphere, was found to be 2.65±0.3 particles/m2 sec sterad. The distribution histogram for the charge spectrum is included. The attenuation mean free paths for three groups were 28.5±2.8, 26.7±2.9, 23.6±3.7 g/cm2 for Z=1011, 1214, 1526, respectively.