The B/C and sub-Iron/Iron Cosmic ray ratios - further evidence in favor of the spiral arm diffusion model

TL;DR

This paper presents evidence supporting a spiral arm diffusion model for cosmic ray propagation, successfully explaining B/C and sub-Fe/Fe ratios with a unified grammage, unlike standard models requiring ad hoc modifications.

Contribution

The study introduces a spiral arm diffusion model that naturally accounts for cosmic ray secondary to primary ratios without ad hoc adjustments, aligning with observational data.

Findings

The spiral arm model explains both ratios with a consistent grammage.

Standard models require inconsistent grammages for different ratios.

The model extends to Nickel, matching observed secondary to primary ratios.

Abstract

The Boron to Carbon (B/C) and sub-Fe/Fe ratios provides an important clue on Cosmic Ray (CR) propagation within the Galaxy. These ratios estimate the grammage that the CR traverse as they propagate from their sources to Earth. Attempts to explain these ratios within the standard CR propagation models require ad hoc modifications and even with those these models necessitate inconsistent grammages to explain both ratios. As an alternative, physically motivated model, we have proposed that CR originate preferably within the galactic spiral arms. CR propagation from dynamic spiral arms has important imprints on various secondary to primary ratios, such as the B/C ratio and the positron fraction. We use our spiral arm diffusion model with the spallation network extended up to Nickel to calculate the sub-Fe/Fe ratio. We show that without any additional parameters the spiral arm model consistently explains both ratios with the same grammage, providing further evidence in favor of this model.