数 GeV/n∿数 TeV/n 領域に於ける重一次宇宙線の観測

概要

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We have exposed a new type of emulsion chamber with full use of the screen-type X-ray film at a level of 11.7g/cm^2 for∿20h, and detected more than hundred thousand cosmic-ray heavy primaries, with charge of Z≳8. This article describes the charge resolution and the accuracy of energy determination for primary cosmic-ray nucleus, and report the absolute intensities of cosmic ray primaries heavier than silicon in the wide energy range, a few GeV/n to TeV/n and beyond. 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 total primary flux, and find that the extrapolation of the direct observation data to the energy region of 10^<15> ∿10^<16>eV/particle deviates slightly from those expected by air shower experiment.
宇宙航空研究開発機構の論文