4.6.1 Advanced peak fitting models

The Gaussian model does not take into account all of the effects involved in the detection of x-rays. The characteristic emission has by itself a Lorentzian distribution to describe the emission energy width, which is often combined with the assumed Gaussian distribution resembling the solid state detector response. However, the contribution of the Lorentzian profile is only noticeable for K-lines with energies greater than 50 keV.

A more close inspection of the peak shape reveals some distinct tail at its low energy part and a shelf extending to zero energy. The incomplete charge collection due to detector imperfections leads to producing pulses with less amplitude, thus deforming the shape of the peak on its lower energy part. Advanced peak fitting models include these contributions.

The parameters of the Lorentzian, the tail and the shelf components can be derived from the experimental calibration of the detector by measuring single emitting element reference materials.