Atomic energy levels, which represent the energy necessary to remove an electron in a given level from the atom, are used for a variety of purposes-from predicting possible interfering x-ray lines in analysis to serving as experimental values with which to compare the results of complicated computer calculations. X-ray wavelength data is essential to determine energy level differences but cannot be used to place the resulting level scheme on an absolute energy basis , X-ray absorption data can be so used but the results of photoelectron energy measurements are superior. Since there are a very large number of possible x-ray lines from a typical element, one can readily obtain many more energy differences than there are energy levels ; hence, to make the best use of the data available, a least squares fitting procedure is used to obtain the most probable value for each energy level,
X-ray wavelengths and x-ray atomic energy levels