INST390 X-Rays

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INST390 X-Rays
2012-11-17 15:47:09

Review of x-rays
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  1. Energy of the x-rays depends on the molecule the atom's in (T/F)
  2. Elements with Z<__ only produce a K series
  3. How are x-rays produced?
    If an inner electron is knocked out of an atom, an electron from a higher energy level will fall (cascade) to take its place. The energy difference is emitted as an x-ray.
  4. Higher accelerating voltage is needed to knock electrons out of an element with a (lower/higher) atomic number
    Higher (Greater positive charge on nucleus of bigger elements; therefore harder to knock electron away)
  5. The name given to an electron dropping from M orbital (2 shells away) to K orbital
    K beta
  6. The name given to an electron dropping from an L orbital (adjacent orbital) to K orbital
    K alpha
  7. 3 ways x-rays are obtained
    • 1. Bombardment of a metal target with a beam of high-energy electrons
    • 2. Exposure of a primary beam of x-rays to generate a secondary fluorescent beam
    • 3. Radioactive decay
  8. What is an angstrom?
  9. Duane Hunt Law
    wavelength (in angstroms) = 12398/V
  10. Accelerating voltage determines ________ used for analysis
  11. XRF
    X-ray Fluorescence
  12. XRD
    X-ray Diffraction
  13. In XRF, the emitted x-ray is (lower/higher) energy than the absorbed x-ray
  14. The energy of the fluoresced X-rays gives you information about:
    What element is present (qualitative analysis)
  15. The number of the fluoresced X-rays produced gives you information about:
    Concentration (quantitative analysis)
  16. WD-XRF
    Wavelength Dispersive X-ray Fluorescence
  17. WD-XRF uses a ___ to separate wavelengths of emitted X-rays
  18. The angle between the incident beam and the scattered beam
    2 theta
  19. 2 Theta (the angle of maximum intensity) is also called
    the Bragg angle
  20. n(wavelength) = 2d sin theta
    Bragg's Law
  21. LIF
    Lithium Fluoride (most common analyzer crystal)
  22. Filters are often used between the ___ and the ____
    • X ray sourcce
    • Sample
  23. In WDXRF the value for ___ is know, and the value for theta is measured in order to determine ___ and therefore the identity of the element
    • d (slit width, since we know what crystal we're using)
    • Wavelength emitted from the sample
  24. The atomic number (Z) for the X-ray source must be ___ than Z for the elements you plan to analyze
  25. After being produced the X-rays in the source pass through a ___ window
  26. the ___ insures the beam of X-rays is parallel
  27. The electron beam in the X-ray sourcce is generated by...
    ...heating a tungsten (W) filament
  28. The term for the rotating table
  29. Sample holders for liquids are typically made of...
    plastic (because it is made up of low atomic number elements which are not affected much by X rays)
  30. Name 4 types of detectors for XRD
    • Film
    • Ionization detector
    • Scintillation Counter
    • Semiconductor
  31. How does a scintillation counter work?
    • X-rays strike a crystal (NAI(Tl))
    • The crystal emits many photons of visible light
    • These photons are detected by a PMT
  32. Why is the crystal of the scintillation counter shileded with aluminum?
    To prevent contamination and water from destroying the crystal
  33. When ionizing radiation passes through a semiconductor detector, it leaves behind a trail of +/- charges in the _____
    depletion zone
  34. 2 main categories of X ray fluorescence analysis. Which is more expensive?
    • Wavelength dispersive (more expensive)
    • Energy dispersive
  35. Which type of X-ray analysis gives us information about the crystal structure of your analyte?
  36. The repeating group of a crystal
    Unit Cell
  37. XRD peak position gives information about
    dimensions fo the unit cell
  38. XRD peak intensity gives information about
    the content of the unit cell (% composition)
  39. XRD peak broadening gives information about
    strain on the crystal
  40. Name 3 things that impact the intensity of an XRD peak
    • crystallographic structure
    • position of the atoms within the unit cell
    • thermal vibration of the atoms
  41. Two main designs for XRD. Which is older?
    • Bragg-Brentano Geometry (uses collimator)
    • Parallel beam optics (using Gobel mirrors and Soller slit)
  42. The name for an equation that gives the minimum wavelength for X-rays produced by hitting a metal with electrons
    Duane-Hunt Law