1 / 19

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

adeola
Download Presentation

Atomic X-Ray Spectrometry

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  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

More Related