The AMS-02 collaboration recently released cosmic-ray F/Si data of
unprecedented accuracy. CR F is predominantly produced by fragmentation of
heavier progenitors, while Si is mostly accelerated at source. This ratio is
thus maximally sensitive to CR propagation. We study the compatibility of the
transport parameters derived from the F/Si ratio with those obtained from the
lighter Li/C, Be/C, and B/C ratios. We also inspect the CR source abundance of
F, one of the few elements with a high first ionisation potential but only
moderately volatile, and a potentially key element to study the acceleration
mechanism of CRs. We use the 1D diffusion model implemented in the USINE code
and perform χ2 analyses accounting for several systematic effects (energy
correlations in data, nuclear cross sections and solar modulation
uncertainties). We also take advantage of the EXFOR nuclear database to update
the F production cross sections for its most important progenitors (identified
to be 56Fe, 32S, 28Si, 27Al, 24Mg, 22Ne, and 20Ne). The transport parameters
obtained from AMS-02 F/Si data are compatible with those obtained from AMS-02
(Li,Be,B)/C data. The combined fit of all these ratios leads to a
χ2/dof≈1.1, with ≲10% adjustments of the B and F
production cross sections (the latter are based on very few nuclear data
points, and would strongly benefit from new measurements). The F/Si ratio is
compatible with a pure secondary origin of F, with a best-fit relative source
abundance 19F/28SiCRS∼10−3 and an upper limit of ∼5×10−3. Unfortunately, this limit is not sufficient to test global
acceleration models of CR nuclei, for which values at the level of ∼10−4 are required. Such levels could be attained with F/Si data of a few
percent accuracy at a few tens of TV, possibly within reach of the next
generation of CR experiments.Comment: 15 pages, 13 figures, 3 table (1 appendix). Submitted to A&