Time dependence of the proton and helium fluxes measured by PAMELA during solar minimum (2006 - 2009)
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Precision measurements of the Z = 2 component in the cosmic radiation provide crucial information about both the origin and propagation of the helium nuclei in cosmic rays inside the Galaxy. Moreover, the precise measurement of the time-dependent helium nuclei fluxes allows an in-depth study of the solar modulation of such nuclei. These results can be compared with the widely studied modulation of protons, to possibly spot dependencies on particle’s charge, mass or local interstellar spectra shape. The helium differential fluxes together with comparison between helium and proton energy spectra, measured by the PAMELA experiment down to 80 MeV, has been studied in the unusually long minimum of solar cycle 23 (July 2006 December 2009) over a 1-month time basis.