  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.
