Figure 1
X-ray fluorescence yield of the naturally occurring elements (Krause, 1979) as a function of the energy of the emitted photon. To detect fluorescence from a given element, one must excite the atom through absorption of a photon with an energy sufficient to eject an electron from a given X-ray `shell' or atomic orbital. The process that competes with fluorescence emission, Auger electron emission, is not well suited to elemental detection in thick biological specimens because Auger electrons tend not to escape at their original element-specific energy except from regions within about 100 nm of the sample's surface. While notable success has been achieved in X-ray fluorescence microscopy of light elements (Kaulich et al., 2009), their low fluorescence yield and strong self-absorption make detection difficult with consequently higher radiation dose imparted. |