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X-Rays

  • Joseph I. Goldstein
  • Dale E. Newbury
  • Joseph R. Michael
  • Nicholas W. M. Ritchie
  • John Henry J. Scott
  • David C. Joy
Chapter

Abstract

Energetic beam electrons stimulate the atoms of the specimen to emit “characteristic” X-ray photons with sharply defined energies that are specific to each atom species. The critical condition for generating characteristic X-rays is that the energy of the beam electron must exceed the electron binding energy, the critical ionization energy Ec, for the particular atom species and the K-, L-, M-, and/or N- atomic shell(s). For efficient excitation, the incident beam energy should be at least twice the critical excitation energy, E0 > 2 Ec. Characteristic X-rays can be used to identify and quantify the elements present within the interaction volume. Simultaneously, beam electrons generate bremsstrahlung, or braking radiation, which creates a continuous X-ray spectrum, the “X-ray continuum,” whose energies fill the range from the practical measurement threshold of 50 eV to the incident beam energy, E0. This continuous X-ray spectrum forms a spectral background beneath the characteristic X-rays which impacts accurate measurement of the characteristic X-rays and determines a finite concentration limit of detection. X-rays are generated throughout a large fraction of the electron interaction volume. The spatial resolution, lateral and in-depth, of electron-excited X-ray microanalysis can be roughly estimated with a modified Kanaya–Okayama range equation or much more completely described with Monte Carlo electron trajectory simulation. Because of their generation over a range of depth, X-rays must propagate through the specimen to reach the surface and are subject to photoelectric absorption which reduces the intensity at all photon energies, but particularly at low energies.

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Copyright information

© Springer Science+Business Media LLC 2018

Open Access This chapter is licensed under the terms of the Creative Commons Attribution-NonCommercial 2.5 International License (http://creativecommons.org/licenses/by-nc/2.5/), which permits any noncommercial use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license and indicate if changes were made.

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Authors and Affiliations

  • Joseph I. Goldstein
    • 1
  • Dale E. Newbury
    • 2
  • Joseph R. Michael
    • 3
  • Nicholas W. M. Ritchie
    • 2
  • John Henry J. Scott
    • 2
  • David C. Joy
    • 4
  1. 1.University of MassachusettsAmherstUSA
  2. 2.National Institute of Standards and TechnologyGaithersburgUSA
  3. 3.Sandia National LaboratoriesAlbuquerqueUSA
  4. 4.University of TennesseeKnoxvilleUSA

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