SpectroscopIC aNALYSIS Part 7 – X-ray Analysis Methods

1. SpectroscopIC aNALYSISPart 7 – X-ray Analysis Methods Chulalongkorn University, Bangkok, Thailand January 2012 Dr Ron Beckett Water Studies Centre & School of ChemistryMonash University, Melbourne, Australia Email: Ron.Beckett@monash.edu Water Studies Centre 1

2. X-ray Analysis Methods • Properties of X-radiation • X-ray diffraction • X-ray emission spectroscopy • Production of X-radiation in an X-ray tube • X-ray fluorscence 2

3. Properties of X-radiation • Frequency n3x1016 – 3x1018Hz • Wavelength l10 nm – 100 pm • High energy radiation, damaging to biological cells • High penetration of materials due to low absorbance is useful in medicine (body X-rays) and material science (fracture detection) 3

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5. X-ray Imaging in Medicine and Dentistry 5

6. X-ray Diffraction by Crystals X-rays are reflected from planes of atoms in the crystal lattice of compounds 6

7. X-ray Diffraction by Crystals X-rays reflected from two planes of atoms in the crystal lattice constructively interfere only when the path length difference is an integral number of wavelengths 7 For waves 1 and 2 path lengths BC + CD = l , 2 l , 3l , ...., n l

8. X-ray Diffraction by Crystals This condition results in the following law for X-ray diffraction by crystals 8

9. X-ray Powder Diffraction Patterns Direction of incident beam Diffracted beams 9 Random orientation of crystals in the powder

10. X-ray Powder Diffraction Camera 10

11. X-ray Powder Diffraction Camera 11

12. X-ray Powder Diffractometer 12

13. X-ray Powder Diffractometer 13

14. X-ray Powder Diffraction Patternsare used to identify crystalline materials and to determine the amount of each phase in a mixture 14

15. Single Crystal X-ray Crystallography Analysis of the geometry and intensity of spots enables the crystal and molecular structure of compounds to be determined 15

16. X-ray Studies Lead to the Discovery of the Double Helix Structure of DNA 16 Rosalyn Franklin Single crystal X-ray pattern of DNA

17. Single Crystal X-ray Diffraction Monochrometers 17

18. Single Crystal X-ray Diffraction Monochrometers 18

19. X-ray Emission Spectrometer Monochrometer Excitation Source electrons protons X-rays g-rays 19

20. X-ray Emission Excitation Source electrons protons X-rays g-rays X-ray Emission

21. X-ray Emission 21

22. X-ray Emission Energy Jumps Emission Excitation Emission 22

23. X-ray Emission Energy Jumps 3d 3p 3s 2p 2s 1s 23

24. X-ray Emission Spectroscopy X-ray emission spectrum of a Ni compound the exact position and intensity of the peaks can give information about the oxidation state and bonding 24

25. Production of X-radiation in an X-ray Tube High voltage extracts electrons from the anode and accelerates them towards the metal cathode These high energy collisions eject electrons from inner atomic orbitals of the metal High Voltage ~100,000 V _ + e- X-radiation Frequency depends on target metal Metal Target

26. Production of X-radiation in an X-ray Tube 26

27. X-ray Tube 27

28. Production of X-radiation in an X-ray Tube . . . . . . . . . . . . High energy electron after collision with metal atom in the target High energy electron accelerated by voltage e- e- e- . Inner shell electron ejected from the metal atom in the target . . . . 28

29. Production of X-radiation in an X-ray Tube . . . . . . . . . . EX-ray = hn = DEelectron 29

30. X-ray Fluorescence AtomicFluorescence Excitation by X-rays ejects electrons from inner orbitals of atoms Electrons from higher orbitals jump back to fill vacancies Emission of fluorescence X-rays occurs Results in Stokes shift to longer wavelength (lower energy since EFluorescence <EExcitation). EExcitation = hnEx e- KE = 1/2mv2 EFluorescence = hnFl e- e- 30

31. X-ray Fluorescence Instrument X-ray Excitation Source Monochrometer X-ray Tube _ e- + Detector EExcitation = hnEx X-ray Emission EFluorescence = hnFl Sample

32. X-ray Fluorescence Spectrometer 32

33. X-ray Fluorescence Analysis • The fluorescence frequencies can be used to identify the elements in the sample • The intensity of the fluorescent X-ray beam is used to determine the concentration of specific elements using callibration standards

34. Thank You for your Attention !