Rigidity dependence of cosmic-ray escape length obtained from a comparison of proton and iron spectra in the energy range 3–3000 GeV

A simple leaky-box model of cosmic-ray propagation in the Galaxy is quite suitable for analysis of cosmic-ray nuclei energy spectra and composition at energies under 1 GeV [1, 2]. Within this model the full information about the cosmic-ray propagation in the Galaxy is compressed into a single parameter, viz., escape length, $X_e$, which characterizes the mean grams of matter that are passed by cosmic-rays from sources to the Earth. In this paper we analyze the worldwide data on proton and iron cosmic-ray spectra that have been collected in experiments and obtain the rigidity dependence of the escape length from the measured rigidity dependence of the proton/iron ratio. This agrees well with the one estimated by a standard manner from the secondary/primary nuclei ratio. However, at ${R>300}$ GV the behavior of $X_e(R)$ distinctly changes, which can point to a change of the proton/iron ratio in cosmic-ray sources.