Editing X-ray fluorescence (section)

===Primary radiation sources===
In order to excite the atoms, a source of radiation is required, with sufficient energy to expel tightly held inner electrons. Conventional [[X-ray generator]]s, based on [[electron]] bombardment of a heavy metal (i.e. [[tungsten]] or [[rhodium]]) target are most commonly used, because their output can readily be "tuned" for the application, and because higher power can be deployed relative to other techniques. X-ray generators in the range 20–60 kV are used, which allow excitation of a broad range of atoms. The continuous spectrum consists of "[[bremsstrahlung]]" radiation: radiation produced when high-energy electrons passing through the tube are progressively decelerated by the material of the tube anode (the "target"). A typical tube output spectrum is shown in Figure 3.

For portable XRF spectrometers, copper target is usually bombared with high energy electrons, that are produced either by impact laser or by pyroelectric crystals.<ref>Kawai, Jun. "Pyroelectric X-Ray Emission." X-Ray Spectroscopy for Chemical State Analysis. Singapore: Springer Nature Singapore, 2022. 107-133.</ref><ref>{{Cite journal|url=https://pubs.aip.org/aip/jap/article-abstract/97/10/104916/317055/High-energy-x-ray-production-with-pyroelectric?redirectedFrom=fulltext|title=High-energy x-ray production with pyroelectric crystals &#124; Journal of Applied Physics &#124; AIP Publishing|journal=Journal of Applied Physics |date=11 May 2005 |volume=97 |issue=10 |doi=10.1063/1.1915536 |last1=Geuther |first1=Jeffrey A. |last2=Danon |first2=Yaron }}</ref>

Alternatively, gamma ray sources, based on [[radioactive isotopes]] (such as <sup>109</sup>Cd, <sup>57</sup>Co, <sup>55</sup>Fe, <sup>238</sup>Pu and <sup>241</sup>Am) can be used without the need for an elaborate power supply, allowing for easier use in small, portable instruments.<ref>{{Cite journal | url=https://inis.iaea.org/collection/NCLCollectionStore/_Public/02/006/2006036.pdf | title=Radioisotope X-Ray Fluorescence Spectrometry | journal=Technical Reports Series | number=115 }}</ref>

When the energy source is a [[synchrotron]] or the X-rays are focused by an optic like a [[polycapillary]], the X-ray beam can be very small and very intense. As a result, atomic information on the sub-micrometer scale can be obtained.