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Atomic number is essentially a characteristic of an atom and has a value that is unique to each chemical element. Table 948 lists the atomic number of the elements in the periodic table.
Table 948. Atomic number of the elements in the periodic table.
Many materials are not a single chemical element, but a conglomerate of compounds and mixtures. For a compound, effective atomic number (Zeff) can be obtained by different methods of calculations. 
Case A. EELS measurement
An appropriate model needs to be used for a different purpose, especially for a compound. In EELS analysis, a model based on Lenz model is applied. In this model, the atomic number can be approximated
using an effective atomic number Zeff, [2, 4]
Equation 948a can be computed with a DM script. Note that for approximate EELS calculations, an estimate of the 'mean' Z of the region under investigation can often suffice.
Case B. ADF STEM measurement
For ADF STEM, its intensity, I, can be given by,
Case C. Three γ-ray processe
The three γ-ray processes for a single element,, namely photoelectric, Compton and pair production, can be given as a function of photon energy hν and the effective atomic number Zeff of the elements.  The interaction is proportional to Zn where n is different for the three processes. Based on Mayneord formula, this effective atomic number Zeff can be given by, 
The exponent, 2.94, in Equation [948d is derived from the relationship between x-ray interactions and atomic number.
Equation 948d can be computed with a DM script.
 Z. Kaliman, N. Orlic and I. Jelovica, Calculations of effective atomic number, Nuclear Instruments and Methods in Physics Research A, 580, (2007) 40–42.