Unknown at first, these photons

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X-Rays

• Unknown at first, these photons
• from innershell transitions
• have played a vital role in
• materials analysis

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X-Ray Generation

• Where do X-Rays come from?

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Source of X-rays as vacancy filled by cascade of
electrons from lower energy levels
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X-Ray Generation

• X-ray tube
• ? Filament (Tungsten)
• ? Target metal (Cu, Cr)
• ? Electrons are accelerated by a potential
  of about 55,000 Volts

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Continuous X-Ray Spectrum

• 35 keV electrons strike the metal target
• They collide with the electrons in the metal
• Rapid deceleration results in emissions of proton
• Photons with a wide range of energies are emitted
  because the degree of deceleration is different

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Characteristic X-Ray

• The incident e- collides with an e- from a cores
  level (K shell)
• An e- in the core level escapes
• The vacant K shell can be filled by a core
  electron from a higher energy level
• A photon is emitted during this transition
• Specific energies are emitted since the core e-
  energy levels are well-defined

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X-Ray Diffraction

• Waves interact with crystalline structures whose
  repeat distance is about the same the wavelength.
• X-rays scattered from a crystalline structure
  constructively interferes and produces a
  diffracted beam.

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Braggs Law

• n ? 2d sin?
• n integer
• ? wavelength (Å)
• d interatomic spacing (Å)
• ? diffraction angle (?)

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Diffractometer

• A Chiller
• B Regulator
• C Computer
• D Strip chart recorder

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• E X-ray source
• F ? compensating slit
• G Sample chamber
• H Scintillation counter
• J Goniometer

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Diffraction Pattern

• Diffraction patterns are a plot of intensity vs ?

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Sample Type

• Single Crystal
• Sample is placed in a beam and the reflections
  are observed for specific orientations
• Time consuming and difficult to orient the
  crystal

• Powder Sample
• Many small crystallites with random orientations
• Much easier to prepare and one can see
  reflections in all directions

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Analyzing a powder sample
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X-Ray Fluorescence Spectrometry

• What is it?
• How does it work?
• Properties
• Advantages
• Disadvantages

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X-Ray Fluorescence Spectrometry? What is it?

• Instrumental method of qualitative and
  quantitative analysis for chemical elements
• Based on the measurement of the wavelength and
  intensities of elements spectral lines emitted
  by secondary excitation

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X-Ray Fluorescence Spectrometry? How does it
work?

• A beam of sufficiently short-wavelength X
  radiation irradiates the sample
• Excites each chemical element to emit secondary
  spectral lines
• Spectral lines have wavelengths characteristics
• This process is known as the secondary excitation

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X-Ray Fluorescence Spectrometry? How does it
work? (continued)

• Sample can have practically any form
• Sample size and shape can be largely varied
• The material to be analyzed can be almost
  anything

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X-Ray Fluorescence Spectrometry? Properties

• The intensities of the resulting fluorescent
  X-rays are smaller
• The method is feasible only when high-intensity
  X-ray tubes, very sensitive detectors and
  suitable X-ray optics are available
• A certain number of quanta can reduce the
  statistical error of the measurement

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X-Ray Fluorescence Spectrometry ? Properties
(continued)

• Intensity influence the time that will be
  necessary to measure a spectrum
• The sensitivity of the analysis depend on the
  peak-to-background ratio of the spectral lines
• Few cases of spectral interference occur

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X-Ray Fluorescence Spectrometry? Advantages

• X-ray spectra is simple and regular
• Matrix effect in X-ray emission are systematic,
  predictable and readily evaluated
• X-ray fluorescence spectroscopy is
  non-destructive.

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X-Ray Fluorescence Spectrometry? Disadvantages

• Small surface layer contributes to the observed
  X-ray line intensity
• Not all of the elements in a sample can be
  measured using the same X-ray tube, crystals, and
  detector

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X-ray Applications

• Electron Microprobe
• Scattering
• Absorptiometry
• Radiography
• Fluoroscopy

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Electron Microprobe

• Nondestructive
• determines composition of tiny amounts of solids.
• Virtually all elements can be analyzed except
  hydrogen helium and lithium.

An Electron Microprobe
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Scattering

• A fluorescence spectrometer is used on a gas,
  liquid, colloidal suspension or solid.
• Coherent and Incoherent scattering rays.
• Ratio of these rays are analyzed.
• Measures radius of gyrations.
• Widely used in proteins, viruses, catalysts,
  hardening and precipitation in alloys and lattice
  deformation.

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Absorptiometry

• Chemical analysis is possible for gases, lipids
  or solids to measure densities porosities as well
  as coating, plating and insulation thickness.
• Most often applied to living patients in
  measurements of bone densities, iodine in the
  thyroid gland, liver diseases and other medical
  uses.
• Two types Single and Dual X-ray Absorptiometry.

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Single X-ray Absorptiometry

• Single X-ray absorptiometry is used to measure
  the bone mineral content.
• Used for diagnosis of osteoporosis, providing
  reasonable accuracy and precision and low
  radiation exposure.

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Dual X-ray Absorptiometry

• Used when single X-ray absorptiometry is not
  feasible.
• Used in areas with variable soft tissue and
  composition such as the spine, hip or the whole
  body.

A Dual X-ray Absorptiometry
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Radiography

• Involves use of registration on film of the
  differential absorption of a beam passing through
  a specimen.
• Medical uses.
• Industrial uses.
• Nondestructive method.

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Fluoroscopy

• Similar to radiography except the image is
  registered on a fluorescent screen.
• Instantaneous and permits observation of internal
  motions and other changes.

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Auger electron spectrometer