Low-energy cosmic-ray heavy nuclei during the time of solar minimum

Nuclear emulsions were exposed at 2.3 g cm−2 atmospheric depth over Fort Churchill in 1965. These emulsions have been examined for the tracks of multiply-charged [Formula: see text] nuclei, with emphasis being paid particularly to those particles that stopped in the emulsions. Differential energy spectra of α particles and [Formula: see text], [Formula: see text]and [Formula: see text] nuclei were obtained in the energy interval 60–550 MeV/nucleon. They represent experimental results during the period when solar modulation effects were at a minimum. The fluxes of α particles and L, M, and H nuclei for energy intervals of 60–170, 100–400, 100–525, and 140–550 MeV/nucleon were found to be 20.9 ± 1.2, 2.4 ± 0.4, 4.8 ± 0.6, and 2.5 ± 0.4 particles m−2 sr−1 s−1, respectively. The results also show that the L/M and H/M ratios at the top of the atmosphere were 0.56 ± 0.16 and 0.34 ± 0.13 respectively, in the energy range from 140 to 350 MeV/nucleon. These values are appreciably greater than those observed at higher energies.