"Quasidirect" observations of cosmic-ray primaries in the energy region1012-1014eV

We have exposed an emulsion chamber at a level of 32.8 g/${\mathrm{cm}}^2$ for ∼30 h, and detected ∼800 showers on x-ray films (Fuji No. 200 type). Among these, ∼200 primaries ($\Sigma E_{\gamma }\ge 2$ TeV, $\theta <75\mathrm{}°$) were identified by tracing back through successive plates of nuclear emulsion. On the basis of these primaries, we obtain $I_p(\ge E_0)=1.02\mathrm{}\times {10}^{-5\mathrm{}}{\left[\frac{E_0}{\left(1\mathrm{} \mathrm{TeV}\right)}\right]}^{-1.82\mathrm{}\pm 0.13}$ ${\left({\mathrm{cm}}^2\mathrm{s}\mathrm{e}\mathrm{c}\mathrm{s}\mathrm{r}\right)}^{-1\mathrm{}}$ in the region $5\lesssim E_0\lesssim 100$ TeV for proton primaries, and $I_{\alpha }(\ge E_0)=6.50\mathrm{}\times {10}^{-7\mathrm{}}{\left[\frac{E_0}{(1\mathrm{} \mathrm{TeV}/\mathrm{nucleon})}\right]}^{-1.75\mathrm{}\pm 0.15}$ ${\left({\mathrm{cm}}^2\mathrm{s}\mathrm{e}\mathrm{c}\mathrm{s}\mathrm{r}\right)}^{-1\mathrm{}}$ in the region $3\lesssim E_0\lesssim 10$ TeV/nucleon for $\alpha$ primaries. We observed also many atmospheric secondary $\gamma$ rays, which cover the energy region 2-80 TeV. The $\gamma$-ray spectrum is a rather smooth continuation of that obtained by Nishimura et al. in the region 0.2-2 TeV. The higher-energy part of our flux, however, cannot be reproduced by the atmospheric nuclear interaction of the primary protons and $\alpha$ particles alone, indicating that, for energies ≳${10}^{14}$ eV/nucleus, the contribution of heavier primaries becomes significant, and that the latter flux may very well become comparable with the proton flux somewhere between ${10}^{14}$ and ${10}^{15}$ eV/nucleus. This indication is consistent with the iron flux obtained directly by the present experiment, though poor statistics preclude a conclusive result.