1. Chapter 12 Atomic X-Ray Spectroscopy

2. is based on measurement of emission,
X-ray spectroscopy, like optical spectroscopy,
is based on measurement of emission,
absorption, scattering, fluorescence,
and diffraction of electromagnetic radiation. X-ray
fluorescence and X-ray absorption methods are
widely used for the qualitative and quantitative
determination of all elements in the periodic table
having atomic numbers greater than that of sodium.
With special equipment, elements with atomic numbers in the range of 5 to 10 can also be determined.

3. 12A FUNDAMENTAL PRINCIPLES

4. X-Rays are short wavelength electromagnetic radiation produced by the deceleration of high-energy electrons or by electronic transitions of electrons in the inner orbitals of atoms.

5. 12A-1 Emission of X-Rays

6. For analytical purposes, X-rays are obtained in four ways: 1
For analytical purposes, X-rays are obtained in four ways: 1. by bombardment of a metal with a beam of high-energy electrons, 2. by exposure of a substance to a primary beam of X-rays in order to generate a secondary beam of X-ray fluorescence, 3. by use of a radioactive source whose decay process results in X-ray emission, 4. from a synchrotron radiation source.

7. Continuum Spectra from Electron Beam Sources

8. V: accelerating voltage e: charge on electron
Ee = E’e + h
At o, E’e = 0
h0 = hc/o = Ve
V: accelerating voltage
e: charge on electron
l0 = 12,398/V
Duane-Hunt Law
Independent of material
Related to acceleration voltage  E l0
FIGURE Distribution of continuum radiation from an
X-ray tube with a tungsten target. The numbers above the
curves indicate the accelerating voltages.

9. FIGURE 12-2 Line spectrum for an X-ray with a molybdenum target.
From electron transitions involving inner shells
Atomic number >23
2 line series K and L
E K> EL
Atomic number < 23
K only
A minimum acceleration voltage is required for
FIGURE Line spectrum for an X-ray with a molybdenum target.
A minimum acceleration voltage required for each element increases
with atomic number

10. Line Spectra from Electron Beam Sources

12. FIGURE Partial energy level diagram showing common transitions producing X-rays. The most intense lines are indicated by the wider arrows.

14. Line Spectra from Fluorescent Sources
Spectra from Radioactive Sources
X-Radiation is often a product of radioactive decay processes.

15. TABLE 12-2
Common Radio isotopic Sources for X-ray Spectroscopy

17. 12A-2 Absorption Spectra
When a beam of X-rays is passed through a thin layer of matter, its intensity or power is generally diminished as a consequence of absorption and scattering.
The absorption spectrum of an element, like its emission spectrum, is simple and consists of a few well-defined absorption peaks.

18. The Absorption Process
The Mass Absorption Coefficient

19. X-ray absorption spectra for lead and silver.
Ln P0/P = μX
μ is the linear
absorption coefficient
is characteristic of the
Element and # of atoms in the path of the beam.
X is sample thickness
Ln P0/P = μMηX
η is density of the sample
μM is mass absorption coefficient
FIGURE 12-5
X-ray absorption spectra for lead and silver.

20. 12A-3
X-ray Fluorescence

21. 12A-4
Diffraction of X-rays

22. Bragg's Law

24. 12B INSTRUMENT COMPONENTS

25. 12B-1 Sources

26. The X-ray Tube
Radioisotopes
Secondary Fluorescent Sources

27. Determining the energy of the X-Ray
100KV!
Controlling the intensity of X-Ray

28. 12B-2
Filters for X-rays

30. 12B-3
X-ray Monochromators

31. FIGURE 12-9 An X-ray monochromator and detector.
Note that the angle of the detector with respect to the
beam (2ө) is twice that of the crystal face. For absorption
analysis, the source is an X-ray tube and the
sample is located in the beam as shown. For emission
measurements, the sample becomes a source of X-ray
fluorescence as shown in the insert.

33. 12B-4 X-ray Transducers and Signal Processors

34. Photon Counting
Gas-Filled Transducers
The Geiger Tube

37. Proportional Counters Ionization Chambers Scintillation Counters
Semiconductor Transducers

38. FIGURE 12-12 Vertical cross section of a
lithium-drifted silicon detector for X-rays
and radiation from radioactive sources.

39. Distribution of Pulse-Heights from X-ray Transducers

40. 12B-5
Signal Processors

41. Pulse-Height Selectors
Pulse-Height Analyzers
Scalers and Counters

43. 12C X-RAY FLUORESCENCE METHODS

44. 12C-1 Instruments

45. Wavelength-Dispersive Instruments
Energy-Dispersive Instruments

46. FIGURE 12-14 Energy-dispersive X-ray fluorescence spectrometer
FIGURE Energy-dispersive X-ray fluorescence spectrometer. Excitation by X-rays from
(a) an X-ray tube and (b) a radioactive substance

48. FIGURE 12-15

49. Semi quantitative Analysis
12C-2 Qualitative and
Semi quantitative Analysis

50. FIGURE X-Ray fluorescence spectrum for a genuine bank note recorded with a wave- length dispersive spectrometer.

51. FIGURE Spectrum of an iron sample obtained with an energy-dispersive instrument with a Rh anode X-ray tube source. The numbers above the peaks are energies in keV. (Reprinted with permission from J. A. Cooper, Amer. Lab., 1976,8 (11),44. Copyright 1976 by International Scientific Communications, Inc.)

52. 12C-3 Quantitative Analysis

53. Calibration Against Standards Use of Internal Standards
Matrix Effects
Calibration Against Standards
Use of Internal Standards
Dilution of Samples and Standards

54. Some Quantitative Applications of X-ray Fluorescence
Advantages and Disadvantages
of X-ray Fluorescence Methods

55. 12D X-RAY ABSORPTION METHODS

56. 12E X-RAY DIFFRACTION METHODS

57. 12E-1 Identification of Crystalline Compounds

58. Automatic Diffractometers
Photographic Recording

59. FIGURE Schematic of (a) a Debye- Scherrer powder camera; (b) the film strip after development. D2, D1 and T indicate positions of the film in the camera.

60. 12E-2 Interpretation of Diffraction Patterns

61. 12F THE ELECTRON MICROPROBE