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Chemical composition of primary cosmic rays with energies from 10 to 10 eV |
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| Authors: | Y Shirasaki F Kakimoto S Ogio N Gironda M Takeda T Kaneko H Yoshii T Baba S Sano K Nishi N Tajima Y Yamada S Shimoda H Nakatani E Gotoh K Murakami Y Toyoda Y Matsubara Y Mizumoto W Velasquez A Velarde P Miranda |
| Institution: | aDepartment of Physics, Tokyo Institute of Technology, Meguro, Tokyo 152-8551, Japan bThe Institute of Physical and Chemical Research, Wako, Saitama 351-0198, Japan cDepartment of Physics, Okayama University, Okayama 700-8530, Japan dDepartment of Physics, Ehime University, Matsuyama, Ehime 790-8577, Japan eNagoya University of Foreign Studies, Nissin, Aichi 470-0197, Japan fFaculty of General Education, Fukui University of Technology, Fukui 910-8505, Japan gSolar-Terrestrial Environment Laboratory, Nagoya University, Nagoya, Aichi 464-8601, Japan hNational Astronomical Observatory, Mitaka, Tokyo 181-8588, Japan iInstituto de Investigaciones Fisicas, Universidad Mayor de San Andres, La Paz 8635, Bolivia |
| Abstract: | The chemical composition of primary cosmic rays with energies from 1015 to 1016.5 eV, so called “knee” region, is examined. We have observed the time structures of air ?erenkov light associated with air showers at Mt. Chacaltaya, Bolivia, since 1995. The distribution of a parameter that characterizes the observed time structures is compared with that calculated with a Monte Carlo technique for various chemical compositions. Then the energy dependence of the average logarithmic mass numbers  ln A of the primary cosmic rays is determined. The present result at 1015.3 eV is almost consistent with the result of JACEE (A 12) and shows gradual increase in ln A as a function of the primary energy (A24 at 1016 eV). Form the comparison of the observational results with several theoretical models, we conclude that the supernova explosion of massive stars is a plausible candidate for the origin of cosmic rays around the “knee” region. |
| Keywords: | Cosmic rays Composition Extensive air showers |
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