Chemical element of metals. Cu comes from Cuprum, Fe comes from Ferrum, Ag from Argentum. The symbols were not followed by a period (full stop) as with abbreviations. Later chemical elements were also assigned unique chemical symbols, based on the name of the element, but not necessarily in English. For example, sodium has the chemical symbol 'Na' after the Latin "natrium". The same applies to "W" (wolfram) for tungsten, "Fe" (ferrum) for iron, "Hg" (hydrargyrum) for mercury, "Sn" (stannum) for tin, "K" (kalium) for potassium, "Au" (aurum) for gold, "Ag" (argentum) for silver, "Pb" (plumbum) for lead, "Cu" (cuprum) for copper, and
Effective atomic number possible to obtain a much more accurate single-valued Z by weighting against the spectrum of the source. The effective atomic number for electron interactions may be calculated with a similar approach; see for instance Taylor "et al." 2009 and Taylor 2011. The cross-section based approach for determining Z is obviously much more complicated than the simple power-law approach described above, and this is why freely-available software has been developed for such calculations (Taylor "et al." 2012). Effective atomic number Effective atomic number has two different meanings: one that is the effective nuclear charge of an atom, and one that calculates