Observation of heavy cosmic‐ray primaries over the wide energy range from GeV/n to TeV/n

We have exposed a new type of emulsion chamber with full use of the screen‐type X‐ray film at a level of 11.7 g/cm2 for ∼20 h, and detected more than hundred thousand cosmic‐ray heavy primaries with charge of Z≳8.Our results of iron and silicon fluxes are both in agreement with those obtained recently by spacelab‐2 experiment. It is particularly remarkable that the spectrum of silicon primaries becomes softer beyond the hundred GeV/n, with integral index of β∼1.95, which is hard to understand in the framework of current models for interstellar propagation as well as for acceleration mechanism. On the other hand, we found that the exponent of iron spectrum is almost constant with β∼1.5 up to a few TeV/n.We report also about the abundance ratio of sub‐iron group to iron, which reflects strongly on the escape length of cosmic rays in the Galaxy. We discuss further the all particle spectrum, and find that the extrapolation of the direct observation data to the energy region of 1015∼1016 eV/particle deviates s...