Energy Loss of Cosmic Rays in the Interplanetary Medium

The expansion of the solar wind is likely to cause low-energy cosmic-ray particles to lose a significant fraction of their energy in the interplanetary medium. It is shown that because of this effect, most of the protons observed below \ensuremath{\sim}100 MeV and alpha particles below \ensuremath{\sim}60 MeV/nucleon originate at higher energies, making it impossible to sample directly the interstellar spectra at these energies.