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

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Abstract

We have exposed an emulsion chamber at a level of 32.8 g/${\mathrm{cm}}^{2}$ for \ensuremath{\sim}30 h, and detected \ensuremath{\sim}800 showers on x-ray films (Fuji No. 200 type). Among these, \ensuremath{\sim}200 primaries ($\ensuremath{\Sigma}{E}_{\ensuremath{\gamma}}\ensuremath{\ge}2$ TeV, $\ensuremath{\theta}<75\ifmmode^\circ\else\textdegree\fi{}$) were identified by tracing back through successive plates of nuclear emulsion. On the basis of these primaries, we obtain ${I}_{p}(\ensuremath{\ge}{E}_{0})=1.02\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}{[\frac{{E}_{0}}{(1 \mathrm{TeV})}]}^{\ensuremath{-}1.82\ifmmode\pm\else\textpm\fi{}0.13}$ ${({\mathrm{cm}}^{2}\phantom{\rule{0ex}{0ex}}\mathrm{s}\mathrm{e}\mathrm{c}\phantom{\rule{0ex}{0ex}}\mathrm{s}\mathrm{r})}^{\ensuremath{-}1}$ in the region $5\ensuremath{\lesssim}{E}_{0}\ensuremath{\lesssim}100$ TeV for proton primaries, and ${I}_{\ensuremath{\alpha}}(\ensuremath{\ge}{E}_{0})=6.50\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}7}{[\frac{{E}_{0}}{(1 \mathrm{TeV}/\mathrm{nucleon})}]}^{\ensuremath{-}1.75\ifmmode\pm\else\textpm\fi{}0.15}$ ${({\mathrm{cm}}^{2}\phantom{\rule{0ex}{0ex}}\mathrm{s}\mathrm{e}\mathrm{c}\phantom{\rule{0ex}{0ex}}\mathrm{s}\mathrm{r})}^{\ensuremath{-}1}$ in the region $3\ensuremath{\lesssim}{E}_{0}\ensuremath{\lesssim}10$ TeV/nucleon for $\ensuremath{\alpha}$ primaries. We observed also many atmospheric secondary $\ensuremath{\gamma}$ rays, which cover the energy region 2-80 TeV. The $\ensuremath{\gamma}$-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 $\ensuremath{\alpha}$ particles alone, indicating that, for energies \ensuremath{\gtrsim}${10}^{14}$ 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.

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