Measurements of 0.2-20 GeV/n cosmic-ray proton and helium spectra from 1997 through 2002 with the BESS spectrometer

We measured low energy cosmic-ray proton and helium spectra in the kinetic energy range 0.215-21.5 GeV/n at different solar activities during a period from 1997 to 2002. The observations were carried out with the BESS spectrometer launched on a balloon at Lynn Lake, Canada. A calculation for the correction of secondary particle backgrounds from the overlying atmosphere was improved by using the measured spectra at small atmospheric depths ranging from 5 through 37 g/cm(2). The uncertainties including statistical and systematic errors of the obtained spectra at the top of atmosphere are 5-7% for protons and 6-9% for helium nuclei in the energy range 0.5-5 GeV/n. (C) 2007 Elsevier B.V. All rights reserved.