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Figure 2868a presents the plasmon energy E_{p} and the energies of relevant coreloss transitions. For light elements (Z<20), the coreloss energies are relatively large (hundreds of eV) and thus do not significantly affect the total EELS intensity. In this case, the scattering is dominated by plasmons and the characteristic EEL energy E_{C} is close to E_{p}. For heavy elements (Z>20), the contribution of the lowenergy coreloss transitions becomes significant thus the difference between E_{C} and E_{p} is increased. The largest difference is located at Z~29, 48, and 79 for the elements with completed outer d shells, but those atoms do not show lowenergy coreloss edges.
The characteristic EEL energies E_{C} is given by, [1]
 [2868]
where,
S(E)  The singlescattering EEL spectrum.
Figure 2868a. Energy of the coreloss (open symbols), energy of plasmon (E_{p}) transitions (solid squares), and a characteristic EEL energy E_{C} (black solid line).
[1]
Figure 2868b shows the plasmon and lowenergy coreloss peaks of yttrium (Y) and palladium (Pd). For the case of Y, the plasmon and coreloss peak can well be separated by spectra fitting with a polynomial function, while for the case of Pd with completed d shells its plasmon peak (~8 eV) is accompanied by a number of other features and their separation can hardly be achieved unambiguously. Those features of Pd probably correspond to different excitations of the composite outer shell consisting of different 4d+5s+5p electronic configurations [1]. Therefore, this interpretation suggests that the number of valence electrons per atom involved in plasmon scattering is larger than number of electrons taking part in chemical reactions.
Figure 2868b. Two representative examples (for Y and Pd) of separating the plasmon and lowenergy coreloss contributions in the EEL spectra.
[1]
[1] Konstantin Iakoubovskii, Kazutaka Mitsuishi,Yoshiko Nakayama, and Kazuo Furuya, Mean free path of inelastic electron scattering in elemental solids and oxides using transmission electron microscopy: Atomic number dependent oscillatory behavior, Physical Review B 77, 104102 (2008).
