Cosmic-ray proton and helium spectra from the first cream flight

Y. S. Yoon, H. S. Ahn, P. S. Allison, M. G. Bagliesi, J. J. Beatty, G. Bigongiari, P. J. Boyle, J. T. Childers, N. B. Conklin, S. Coutu, M. A. Duvernois, O. Ganel, J. H. Han, J. A. Jeon, K. C. Kim, M. H. Lee, L. Lutz, P. Maestro, A. Malinine, P. S. MarrocchesiS. A. Minnick, S. I. Mognet, S. Nam, S. Nutter, I. H. Park, N. H. Park, E. S. Seo, R. Sina, S. Swordy, S. P. Wakely, J. Wu, J. Yang, R. Zei, S. Y. Zinn

Research output: Contribution to journalArticlepeer-review

190 Scopus citations


Cosmic-ray proton and helium spectra have been measured with the balloon-borne Cosmic Ray Energetics And Mass experiment flown for 42 days in Antarctica in the 2004-2005 austral summer season. High-energy cosmic-ray data were collected at an average altitude of ∼38.5 km with an average atmospheric overburden of ∼3.9 g cm-2. Individual elements are clearly separated with a charge resolution of ∼0.15 e (in charge units) and ∼0.2 e for protons and helium nuclei, respectively. The measured spectra at the top of the atmosphere are represented by power laws with a spectral index of -2.66 ± 0.02 for protons from 2.5 TeV to 250 TeV and -2.58 ± 0.02 for helium nuclei from 630 GeV nucleon-1 to 63 TeV nucleon -1. They are harder than previous measurements at a few tens of GeV nucleon-1. The helium flux is higher than that expected from the extrapolation of the power law fitted to the lower-energy data. The relative abundance of protons to helium nuclei is 9.1 ± 0.5 for the range from 2.5 TeV nucleon-1 to 63 TeV nucleon-1. This ratio is considerably smaller than the previous measurements at a few tens of GeV nucleon-1.

Original languageEnglish (US)
JournalAstrophysical Journal
Issue number2
StatePublished - Feb 20 2011

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


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