2-d histogram of (a) proton-downward proton matrix and (b) proton-downward neutron matrix under a vertical column depth of 20 g/cm². X-axis and Y-axis stand for the input and output energies [MeV] respectively. The vertical line in (a) marks the 150 MeV input proton energy. The probabilities of a proton with certain primary energy producing secondaries with different energies are represented by colors using a logarithmic color distribution. Each column in this plot is equivalent to a normalized output spectrum obtained by PLANETOCOSMICS using protons of the corresponding input energy.