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Atomic X-Ray Spectrometry

Atomic X-Ray Spectrometry. Emission, absorption, scattering, fluorescence and diffraction Fundamentals Instruments X-ray Fluorescence X-ray Absorption X-ray diffraction. Fundamentals. X-rays X-ray wavelengths from 1E-5 angstrom to 100 angstrom De-acceleration of high energy electrons

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Atomic X-Ray Spectrometry

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  1. Atomic X-Ray Spectrometry • Emission, absorption, scattering, fluorescence and diffraction • Fundamentals • Instruments • X-ray Fluorescence • X-ray Absorption • X-ray diffraction

  2. Fundamentals • X-rays • X-ray wavelengths from 1E-5 angstrom to 100 angstrom • De-acceleration of high energy electrons • Electron transitions from inner orbitals • Bombardment of metal with high energy electrons • Secondary x-ray fluorescence by primary x-rays • Radioactive sources • Synchrotron sources

  3. Continuum sources • Cathode produced x-rays • Short wavelength limit (lo) • Dependent upon accelerating voltage, not material • X-ray produced by electron de-acceleration • Line spectra • Requires minimum voltage • Electronic transitions amongst inner atomic orbitals • K and L lines

  4. X-ray generation

  5. Composite X-ray

  6. Absorption Spectra • Edge keV A • K 115.6061 0.1072 • L-I 21.7574 0.5698 • L-II 20.9476 0.5919 • L-III 17.1663 0.7223 • M1 5.5480 2.2348 • M2 5.1822 2.3925 • M3 4.3034 2.8811 • M4 3.7276 3.3261 • M5 3.5517 3.4908 • N1 1.4408 8.6052 • N2 1.2726 9.7426 • N3 1.0449 11.8657 U absorption edges and scattering coefficients

  7. Absorption Ln (P0/P)=mx x is sample thickness Transmitted (P) and incident (P0) beam power • is linear absorption coefficient Linear combinations of elements

  8. X-ray Fluorescence • Emission of x-ray from excited elements • Absorption removes electron • Fluorescence involves inter electron transfers • x-ray can either be absorbed by the atom or scattered • x-ray absorbed by the atom by transferring all of its energy to an innermost electron is photoelectric effect • if primary x-ray has sufficient energy electrons are ejected from inner shells, creating vacancies • electrons from outer shells are transferred to the inner shells resulting in characteristic x-ray • energy is the difference between the two binding energies of the corresponding shells • each element produces x-rays at a unique set of energies • The process of emissions of characteristic x-rays is X-ray Fluorescence (XRF) • innermost K and L shells are involved in XRF detection

  9. X-ray Fluorescence

  10. Diffraction • Interaction between x-rays and electrons in sample • Constructive and destructive interference • Distance between scattering points are on same order as radiation wavelengths • diffraction

  11. Diffraction • Bragg equation • sin q defines observed angles • All others destructive interference

  12. XRD • Fixed wavelength, vary angle • Powder specimen • Grains act as single crystal • Plot I vs angle • At Bragg angle produce angle

  13. Data analysis Normalize data to 1st sin^2theta Clear fractions Speculate on hkl Know wavelength from source, solve for a

  14. Si glass XRD

  15. Transducers • Photon counting • Gas filled counters • Ionization due to photon interaction with gas • Ionization chambers • Geiger counters • Proportional counters • Scintillation counters • Solid state • Ge • NaI

  16. Gas filled counters

  17. Solid state detector 137-Cs

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