The isotopic source composition of cosmic-ray iron, cobalt, and nickel

The isotopic composition of cosmic-ray Fe, Co, and Ni at energies ∼150–500 MeV/nucleon has been measured with the Cosmic-Ray Isotope Spectrometer (CRIS) instrument on ACE. Source abundances have been derived from a leaky-box propagation model using secondary species in the range 41 ≤ A ≤ 55 to constrain the calculated secondary contributions to the Fe, Co, and Ni isotopes. The derived relative source abundances bear a strong resemblance to solar-system values. The most significant difference, an excess of ∼ (70 ± 30)%, is found for the source abundance ratio ^(58)Fe/^(56)Fe. Some implications of the derived source composition for the origin of cosmic rays are discussed