Very Heavy Nuclei in the Primary Cosmic Radiation. I. Observations on the Energy Spectrum

The intensities and energy spectrum of the medium- and very heavy, MH and VH, nuclei, 16≤Z≤30, present in the primary cosmic radiation have been studied using three stacks of nuclear emulsions exposed on high-altitude balloons flown over Fort Churchill (Canada), Texas, and India. Integral intensities of Z≥20 nuclei above energies of 0.225, 1.58, and 7.1 BeV per nucleon were, respectively, 1.50±{}0.06, 0.403±{}0.023, and 0.090±{}0.006 (VH nuclei)/m²sr sec. The energy spectrum of these nuclei was measured in detail between 225 MeV per nucleon and 1 BeV per nucleon, and was found to exhibit a maximum in the 300- to 400-MeV per nucleon range, where the differential intensity was of the order of 1.7×{}10^-3 nuclei/m² sr sec (MeV per nucleon). Integral intensities of 16≤Z≤19 nuclei above energies of 1.58 and 7.1 BeV per nucleon were, respectively, 0.086±{}0.010 and 0.020±{}0.003 nuclei/m² sr sec; differential intensities were also measured at lower energies.