Calculated a) EW and b) luminosity of the 6.4 keV Fe Kα line produced by LECR ions as a function of the path length of the CRs injected in the X-ray production region, for five values of the CR source spectral index s (Eq. (A.7)). The ambient medium is assumed to have a solar composition, and the minimum energy of the CRs that penetrate this medium is E_min = 1 MeV nucleon^-1. In panel b) the luminosity calculations are normalized to a total power of 1 erg s^-1 injected by the fast primary protons in the ambient medium.