Illustration of the parameters that can be determined from the energy-deposition profiles of cosmic-ray nuclei. The dashed curves show the mean energy deposition, (dE/dx), of protons with different energies in high-density polyethylene¹. The energy-deposition profile of a stopping particle encodes its nuclear charge, Z, mass number, A, velocity, β, and kinetic energy, E_kin. For penetrating particles, only Z and β can be determined. The solid curves illustrate how ionization quenching reduces the measurable energy-deposition density, which we denote as (dE/dx)_vis. For clarity, fluctuations due to energy-loss straggling are not shown.