Elemental fraction for four mass groups obtained using the PCS model of EG-CRs and WR-CRs (C/He = 0.1). The proton fraction (not shown in the figure) predicted by the model in the LOFAR energy range is ~ 10%. The grey bands, from top to bottom, represent the best-fit LOFAR measurements of 79% helium, 19% nitrogen and 2% iron nuclei in the energy range of (1.3−4.2) × 10⁸ GeV (Buitink et al. 2016). At 99% confidence level, the measured proton plus helium fraction can vary in the range of (38−98)%, and the combined nitrogen and iron fraction within (2−62)%.