Energy-per-nucleon spectra at ω_cpt = 48.99. The original spectra of different ion species (a) and spectra of heavy ions shifted for visibility on the y-axis by a factor of 10⁰, 10¹, 10², and 10³ for ⁴He²⁺, ³He²⁺, ¹⁶O⁷⁺, and ⁵⁶Fe¹⁴⁺, respectively (b). The dashed lines in the right panel are the power-law fit (E^γ) to the shoulder region of the spectra, where E is the energy-per-nucleon.