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, $\mathrm{MH}$ and $\mathrm{VH}$, nuclei, $16\le Z\le 30$, 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 $Z\ge 20$ 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 ($\mathrm{VH}$ nuclei)/${\mathrm{m}}^2$sr 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×${10}^{-3\mathrm{}}$ nuclei/${\mathrm{m}}^2$ sr sec (MeV per nucleon). Integral intensities of $16\le Z\le 19$ nuclei above energies of 1.58 and 7.1 BeV per nucleon were, respectively, 0.086±0.010 and 0.020±0.003 nuclei/${\mathrm{m}}^2$ sr sec; differential intensities were also measured at lower energies.