Galactic cosmic ray heavy ions in near earth space: Ionization states and their significance

Abstract

The Spacelab-3 cosmic ray experiment Anuradha was successfully flown and operated at an orbital altitude of 350 km and at 57° inclination. In addition to the determination of the ionization states of the anomalous cosmic rays (ACR), this experiment enabled the measurements of ionization states (Z ∗) of galactic cosmic ray (GCR) sub-iron and iron ions (Z=21 – 28) of energy 25–125 MeV/N using the earth's magnetic field as a rigidity filter. From trajectory computations of a total 62 low energy events, Z ∗ was determined for 16 ACR and 46 GCR particles. 16 GCR events of sub-iron and iron ions were found to be in partially ionized states. These partially ionized ions comprising of about 30% of particles form a new subset of low energy (25–125 MeV/N) GCR. It is suggested that GCR sub-iron and iron ions of 1–10 MeV/N capture electrons while traversing interstellar matter and these are reaccelerated in SNR shock fronts in ISM and also in helicspheric boundary to energies of 100–500 MeV/N before entering the inner solar system.