Gamma-ray spectra and triangle representation of the C, N, and O chemical proportions for bare samples of wood (on top), melamine (in the middle), and ammonium acetate (below). The dashed red lines in the energy spectra correspond to the fit with a linear combination of the pure element spectra. The unfolded count fractions are given in % and the reported O/C and N/C are the chemical ratios obtained with the conversion factors calculated for these measurement setups.