X-ray fluorescence
= X-ray fluorescence
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<X-ray fluorescence> is <Characteristic X-ray> emission following excitation by incident <photons>. In a simple initially unexcited <chemical atom>, <photoionization> can eject an inner <Electron> if the incident <photon> supplies its <binding energy>. An outer <Electron> can then fill the vacancy, releasing an emitted <photon> with the difference of shell <binding energies>. Nonradiative relaxation competes with this route, so one absorbed incident <photon> need not yield one escaping characteristic <photon>.
Choose a separate stipulated <electron shell> model with values $B_K=10.0$, $B_L=1.5$ and $B_M=0.3$, all in $\mathrm{keV}$. Ignore subshell splitting, recoil and changes of <binding energy> during relaxation. The possible shell differences are
$$
E_{K\alpha}=B_K-B_L=8.5\,\mathrm{keV},\qquad
E_{K\beta}=B_K-B_M=9.7\,\mathrm{keV},\qquad
E_{L\alpha}=B_L-B_M=1.2\,\mathrm{keV}.
$$
These labels denote simplified shell groups, not resolved subshell <electronic transitions>. With $hc=1.23984\,\mathrm{keV\,nm}$, their calculated <wavelengths> are respectively $0.145864$, $0.127819$ and $1.03320\,\mathrm{nm}$. An incident $9.8\,\mathrm{keV}$ <photon> exceeds both K-line <energies> but cannot directly create the K vacancy in this initially unexcited model. A $12.0\,\mathrm{keV}$ <photon> can, leaving approximately $2.0\,\mathrm{keV}$ of <photoelectron> <kinetic energy>. This comparison fixes neither the excitation probability nor the radiative branching probability.