2011/01/28 by Y. S. Yoon, H. S. Ahn, P. S. Allison +31 · 7 citations
Physics and Astronomy · #Astrophysics and Cosmic Phenomena #Cosmic ray #Dark Matter and Cosmic Phenomena #Flux (metallurgy) #Helium #Isotopes of helium #Power law #Proton #Range (aeronautics) #Solar and Space Plasma Dynamics #Spectral line #astro-ph.HE
paper · pdf · doi:10.1088/0004-637x/728/2/122
published as Astrophys.J.728:122,2011 · 20 pages, 4 figures
openalex publication_date 2011/01/28 · arxiv created 2011/02/13 · arxiv updated 2011/07/28 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
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 .