Spallation-dominated propagation of heavy cosmic rays and the Local Interstellar Medium (LISM)

Measurements of ultra-heavy nuclei at GeV/n energies in the galactic cosmic radiation address the question of their sources (nucleosynthetic s- and r-processes). As such, the determination of CR source abundances is a promising way to discriminate between existing nucleosynthesis models. For primary species (nuclei present and accelerated at the source), it is generally assumed that the relative propagated abundances, if they are close in mass, are not too different from their relative source abundances. The range of the correction factor associated with propagation has been estimated in weighted slab models only. Heavy CRs that are detected near the Earth were accelerated from regions that are closer to us than were the light nuclei. Hence, both the geometry of sources in the Solar neighbourhood, and the geometry of gas in the same region, must be taken into account. In this paper, a two zone diffusion model is used, and as was previously investigated for radioactive species, we report here on the impact of the local interstellar medium (LISM – under-dense medium over a scale ~100 pc) on primary and secondary stable nuclei propagated abundances. Considering down to Fe nuclei, the connection between heavy and light abundances is also inspected. A general trend is found that decreases the UHCR source abundances relative to the HCR ones. This could have an impact on the level of r-processes required to reproduce the data.