Cryo-scanning energy dispersive X-ray microanalysis (CEDX) requires the addition to the CSEM of an energy dispersive X-ray analyser (EDXA). X-rays are continuously emitted from the specimen through scattering between the incident beam electrons and atoms of elements within the sample. This interaction can lead to an ejection of an electron from one of the electron shells (orbits) surrounding the nucleus, leaving a vacancy. An electron from one of the higher energy levels will drop down to fill this void resulting in some excess energy, equivalent to the difference in energy levels between two orbits, being released as an X-ray. The EDXA system is used to collect these X-rays and present the results as a graph displaying X-ray energy versus Intensity. Typically there will be several sets of peaks in the X-ray spectrum each set representing the presence of a particular element. The intensity of a given peak will vary according to the concentration of the element it represents.
This text has been reproduced from McCully et al. Functional Plant Biology (in press) (2010).