Modes of Excitation for XRF Analysis

X-ray fluorescence spectroscopy can be accomplished using (a) radioactive sources as exciters or (b) X-ray tube as exciter. 

Isotope Half-life Energy (keV) Analysis Range 

The influence of the photons emitted by a Am XRF excitation source below 59.6 keV on sample fluorescence production has been analyzed and general method for evaluating the contribution of the various lines from the source in specific equipment configurations is presented by Delgado et al. (1987). A typical L X-ray spectrum of Pb by Am source (Kumar et al. 1999) is presented in Fig. 1.5, which also shows the peaks due to elastically- and inelastically-scattered photons from the Am source. 

The excitation by X-ray sources requires the knowledge about the values of critical excitation energies of different som ces to enable the excitation of inner-shell electrons of various elements present/expected to be present in the sample. Two basic processes i.e., the attenuation and the scattering of X-rays are involved when the intensity is reduced to after the photon beam of intensity lo passes through the material of thickness x. The reduced intensity is given by Lambert law = Iq exp(— o ), where p is called the linear atten- 

The sharp discontinuities in the absorption curve are related to the critical excitation energies (and their corresponding wavelengths) of the element for the K-shell/ Lj, Ln, and Lni subshells of the L-shell/ Mj, Mu, Mm, Mjv, and Mv subshells of the M-shell, etc. The K- and L-shell absorption edges for a few elements given in wavelength (A) by Bearden (1967), converted in keV, 

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