Evidence for Multiply Charged Anomalous Cosmic Rays

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Abstract
New measurements from the SAMPEX spacecraft show that most anomalous cosmic ray (ACR) oxygen nuclei with energies above 20 MeV nucleon-1 are multiply ionized, with ionic charge states of Q = 2, Q = 3, and probably higher. This new result contrasts with lower energies, at which most ACRs are singly charged. The observed abundance of multiply charged ions agrees with estimates of the fraction of singly charged ACRs that undergo electron stripping during acceleration if the timescale for acceleration to 10 MeV nucleon-1 is ~1 yr. The existence of multiply charged ACRs helps explain their acceleration to high energies, and it has implications for several other studies.