  The multi-TeV energy region of the cosmic-ray spectra has been recently
explored by direct detection experiments that used calorimetric techniques to
measure the energy of the cosmic particles. Interesting spectral features have
been observed in both all-electron and nuclei spectra. However, the
interpretation of the results is compromised by the disagreements between the
data obtained from the various experiments, that are not reconcilable with the
quoted experimental uncertainties. Understanding the reason for the discrepancy
among the measurements is of fundamental importance in view of the forthcoming
high-energy cosmic-ray experiments planned for space, as well as for the
correct interpretation of the available results. The purpose of this work is to
investigate the possibility that a systematic effect may derive from the
non-proportionality of the light response of inorganic crystals, typically used
in high-energy calorimetry due to their excellent energy-resolution
performance. The main reason for the non-proportionality of the crystals is
that scintillation light yield depends on ionisation density. Experimental data
obtained with ion beams were used to characterize the light response of various
scintillator materials. The obtained luminous efficiencies were used as input
of a Monte Carlo simulation to perform a comparative study of the effect of the
light-yield non-proportionality on the detection of high-energy electromagnetic
and hadronic showers. The result of this study indicates that, if the
calorimeter response is calibrated by using the energy deposit of minimum
ionizing particles, the measured shower energy might be affected by a
significant systematic shift, at the level of few percent, whose sign and
magnitude depend specifically on the type of scintillator material used.
