Study on origins of cosmic rays with energies above 10^<16>eV

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The purpose of this research is to determine the chemical composition of primary cosmic rays with energies above 10^<16>eV. The observation site is at the laboratory for cosmic ray physics at mount Chacaltaya in Bolivia. This laboratory is situated at 5,200m above the sea level, and then this is the world highest one among the cosmic ray observation sites. In this study we measure equi-intensity curves of cosmic ray air showers. A high altitude experiment enables us to get the curves in wider atmospheric depth. The primary composition reflects deeply on the features of these curves. So that the observed curves are compared with those obtained with a Monte Carlo simulations and then we derive the result.For this study we started to install a new air shower array and finished at the end of 2006. However it took about a half year more for us to reduce the induced noises through the recycled signal cables, which were used at the prior air shower array.From now we observe air showers at least for more five years, and then the final result is obtained.