Observation of low-energy (30-100 MeV nucleon-1) partially ionized heavy ions in galactic cosmic rays

Experimental evidence is presented that shows the existence of low-energy (30-100 MeV/nucleon) partially ionized heavy ions in Galactic cosmic rays. The measurements were made by a CR-39 plastic nuclear detector module aboard the Spacelab-3 mission during the cosmic-ray experiment Anuradha (April 29 - May 6, 1985), in which the ionization states of low-energy cosmic-ray ions of elements O to Fe were determined by utilizing the earth's magnetic field as a momentum analyzer. It was found that, while most of the ions of the Fe group in this energy range were fully ionized, Ti, Cr, and Fe were observed in partially ionized states equal to or lower than 6, 8, and 20, respectively. The possible sources of these particles are discussed. 24 refs.