Impact of transport modeling on the 60Fe abundance inside Galactic cosmic ray sources

The ACE-CRIS Collaboration has recently released the measurement of radioactive ⁶⁰Fe nuclei abundance in Galactic cosmic rays, in the energy range ∼195 - 500 MeV per nucleon. We model cosmic ray propagation and derive from this measurement the ⁶⁰Fe/⁵⁶Fe ratio that is expected in the sources of Galactic cosmic rays. We describe cosmic ray origin and transport within the framework of the disk/halo diffusion model, namely a scenario in which the matter and the cosmic ray sources in our Galaxy are confined to a thin disk, while cosmic ray propagation occurs in a much larger halo with negligible matter density. We solve the cosmic ray transport equation accounting for spallation reactions, decay and ionization losses as well as advection. We find that the ⁶⁰Fe/⁵⁶Fe ratio at the source must be very close to the value detected in the local cosmic ray spectrum at Earth, due to the fact that spallation reactions are more effective for ⁵⁶ than for ⁶⁰Fe. Such a result could help identify the sources of Galactic cosmic rays.