XRF (X-ray fluorescence) By Hossein bandori

XRF (X-ray fluorescence)
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1. XRF ( X - ray fluorescence ) By : Hossein Bandori Kharazmi University Department of Geology

2. X-rays make up X-radiation , a form of electromagnetic radiation . Most X-rays have a wavelength ranging from 0.01 to 10 nanometers , corresponding to frequencies in the range 30 petahertz to 30 exahertz (3×10 16 Hz to 3×10 19 Hz) and energies in the range 100 eV to 100 keV . X-ray wavelengths are shorter than those of UV rays and typically longer than those of gamma rays . In many languages, X-radiation is referred to with terms meaning Röntgen radiation , after the German scientist Wilhelm Röntgen , who usually is credited as its discoverer, and who had named it X-radiation to signify an unknown type of radiation. Spelling of X-ray(s) in the English language includes the variants x-ray(s) , xray (s) , and X ray(s) .

3. X-rays are part of the electromagnetic spectrum , with wavelengths shorter than visible light . Different applications use different parts of the X-ray spectrum.

4. Application of X-Ray

5. X-ray fluorescence X-ray fluorescence ( XRF ) is the emission of characteristic "secondary" (or fluorescent) X-rays from a material that has been excited by bombarding with high-energy X-rays or gamma rays . The phenomenon is widely used for elemental analysis and chemical analysis , particularly in the investigation of metals , glass , ceramics and building materials, and for research in geochemistry , forensic science , archaeology and art objects such as paintings [2] and murals .

6. A Philips PW1606 X-ray fluorescence spectrometer with automated sample feed in a cement plant quality control laboratory

7. In 1925 X-rays were used for the first time to excite a sample, but the technique was only made practical in 1940 and the first commercial XRF spectrometers were produced in 1950. These were based on wavelength dispersive x-ray fluorescence (WDXRF) and measured the wavelength of an element, one element at a time. In the 1960’s energy dispersive x-ray fluorescence (EDXRF) spectrometers began to rival WDXRF. Since the 1960’s XRF spectrometers have progressed greatly and XRF spectrometers was even included on the Apollo 15 and 16 missions.

8. Some of the applications of XRF include: research and development, soil surveys, mining, cement production, ceramic and glass manufacturing, quality control (metallurgy), environmental studies, petroleum industry and field analysis in geological and environmental studies.

9. FUNDAMENTAL PRICIPLES OF XRF XRF works on methods involving interactions between electron beams and x-rays with samples. • Made possible by the behavior of atoms when they interact with radiation. • When materials are excited with high-energy, short wavelength radiation (e.g., X-rays), they can become ionized. • If the energy of the radiation is sufficient to dislodge a tightly- held inner electron, the atom becomes unstable and an outer electron replaces the missing inner electron. • When this happens, energy is released due to the decreased binding energy of the inner electron orbital compared with an outer one.

10. PRINCIPLES CONT’D • The emitted radiation is of lower energy than the primary incident X-rays and is termed fluorescent radiation. • Because the energy of the emitted photon is characteristic of a transition between specific electron orbitals in a particular element, the resulting fluorescent X-rays can be used to detect the abundances of elements that are present in the sample.

11. Excitation of the sample Spectrometer Secondary X-Rays or X- Ray Fluorescence which is characteristic for the elemental composition of the sample Sample

12. An Incoming X-Ray photon strikes an electron, the electron breaks free and leaves the atom. Principle of the excitation by X-Rays

13. Principle of the excitation by X-Rays This leaves a void that must be filled by an electron from an outer shell. The excess energy from the new electron is released (fluorescence) in the form of an x-ray photon. X-Ray Photon X-Ray Fluorescence

14. excitation by X-Rays

15. Excitation and Interactions between shells Layer K Layer L Layer N Layer M

16. Excitation and Interactions between shells Layer K Layer L Layer N Layer M

17. XRF - HOW IT WORKS? • An XRF spectrometer works because if a sample is illuminated by an intense X-ray beam, known as the incident beam, some of the energy is scattered, but some is also absorbed within the sample in a manner that depends on its chemistry.

18. • The incident X-ray beam is typically produced from a Rh target, although W, Mo, Cr and others can also be used, depending on the application. XRF - HOW IT WORKS?

19. XRF - HOW IT WORKS? • When x-ray hits sample, the sample emits x-rays along a spectrum of wavelengths characteristic of the type of atoms present. • Flow counters measure long wavelength(>0.15nm) x-rays typical of elements lighter than zinc. • The scintillation detector is commonly used to analyze shorter wavelengths in the X-ray spectrum(K spectra of element from Nb to I; L spectra of Th and U).

20. • If a sample has many elements present, the use of a Wavelength Dispersive Spectrometer allows the separation of a complex emitted X-ray spectrum into characteristic wavelengths for each element present. • Various types of detectors used to measure intensity of emitted radiation. • Examples of detectors used include the flow counter and the scintillation detector. XRF - HOW IT WORKS?

21. • The intensity of the energy measured by these detectors is proportional to the abundance of the element in the sample. • The exact value for each element is derived from standards from prior analyses from other techniques. XRF - HOW IT WORKS?

22. BOX DIAGRAM OF XRF INSTRUMENT

23. • Minimal or no sample preparation • Non-destructive analysis • Na11 to U92 analysis, ppm to high % concentration range BENEFITS OF XRF ANALYSIS

24. • No wet chemistry – no acids, no reagents • Analysis of solids, liquids, powders, films, granules etc. • Rapid analysis – results in minutes BENEFITS OF XRF ANALYSIS

25. • Qualitative, semi-quantitative, to full quantitative analysis • For routine quality control analysis instrument can be ‘used by anyone’ BENEFITS OF XRF ANALYSIS

26. APPLICATIONS X-Ray fluorescence is used in a wide range of applications, including • research in igneous, sedimentary, and metamorphic petrology • soil surveys • mining (e.g., measuring the grade of ore)

27. • cement production • ceramic and glass manufacturing • metallurgy (e.g., quality control) • environmental studies (e.g., analyses of particulate matter on air filters) APPLICATIONS

28. APPLICATIONS CONT’D • petroleum industry (e.g., sulfur content of crude oils and petroleum products) • field analysis in geological and environmental studies (using portable, hand-held XRF spectrometers) X-ray fluorescence is limited to analysis of • relatively large samples, typically > 1 gram

29. • materials that can be prepared in powder form and effectively homogenized • materials for which compositionally similar, well-characterized standards are available • materials containing high abundances of elements for which absorption and fluorescence effects are reasonably well understood APPLICATIONS CONT’D

30. STRENGTHS & LIMITATIONS OF XRF Strengths X-Ray fluorescence is particularly well-suited for investigations that involve: • bulk chemical analyses of major elements (Si, Ti , Al, Fe, Mn , Mg, Ca, Na, K, P) in rock and sediment • bulk chemical analyses of trace elements (>1 ppm; Ba, Ce, Co, Cr, Cu, Ga, La, Nb , Ni, Rb , Sc , Sr , Rh, U, V, Y, Zr , Zn) in rock and sediment

31. STRENGTHS & LIMITATIONS OF XRF Strengths X-Ray fluorescence is particularly well-suited for investigations that involve: • bulk chemical analyses of major elements (Si, Ti , Al, Fe, Mn , Mg, Ca, Na, K, P) in rock and sediment

32. • bulk chemical analyses of trace elements (>1 ppm; Ba, Ce, Co, Cr, Cu, Ga, La, Nb , Ni, Rb , Sc , Sr , Rh, U, V, Y, Zr , Zn) in rock and sediment STRENGTHS & LIMITATIONS OF XRF

33. LIMITATIONS In theory the XRF has the ability to detect X-ray emission from virtually all elements, depending on the wavelength and intensity of incident x-rays. However... • In practice, most commercially available instruments are very limited in their ability to precisely and accurately measure the abundances of elements with Z<11 in most natural earth materials.

34. • XRF analyses cannot distinguish variations among isotopes of an element, so these analyses are routinely done with other instruments. • XRF analyses cannot distinguish ions of the same element in different valence states, so these analyses of rocks and minerals are done with techniques such as wet chemical analysis or Mossbauer spectroscopy. LIMITATIONS

35. No mater how the secondary X-ray radiation (X-Ray fluorescence) is produced in XRF machines there are TWO WAYS to detect this radiation: XRF detection system

36. ◦ Wavelength Dispersive System (WDS) and ◦ Energy Dispersive System (EDS). XRF detection system

37. A wavelength dispersive detection system physically separates the X-Rays according to their wavelengths. The x-rays are directed to a crystal, which diffracts (according to Bragg´s Law) the X-Rays in different directions according to their wavelengths (energies). WDS

38. XRF: A Powerful Analysis Tool

39. • EDS is an analytical technique used for the elemental analysis or chemical characterization of a sample. • The secondary x-rays (XRF) are directed to a detector. EDS

40. • A detector is used to convert X-ray energy into voltage signals; this information is sent to a pulse processor, which measures the energy of the signals and passes them onto an analyzer. • The analyzer converts the analog into a digital signal which is proportional to the energy of the incoming pulse. EDS

41. • Received pulses are actually amplified and converted into digital signals. • They are sorted by energy with help of multi-channel analyzer (energy is characteristic for each element) and frequency of appearance (characteristic for concentration) and sent to data display and analysis. EDS

42. • The most common detector now is Si(Li) detector cooled to cryogenic temperatures with liquid nitrogen. EDS

43. EDS ED-XRF

44. EDS SEM-EDX

45. Specifically designed for the rigorous demands of nondestructive elemental analysis in the field. HANDHELD XRF

46. • The XRF method of characterization provides a fast and reliable way of acquiring information on; the elementary composition and chemical state. CONCLUSION

47. THE End