XRay Analysis

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X-Ray Analysis
Homework for chapter 12 12-1, 12-2, 12-9, 12-10
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X-Ray Spectroscopy

• Emission (fluorescence)
• Absorption
• Diffraction
• X-Ray photoelectron spectroscopy

Beers law
Thickness of the sample
Linear absorption coefficient
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X-Ray Spectroscopy

• X-Ray wavelengths
• 10-5 A 100 A

o
o
Wavelengths used in X-Ray Spectroscopy
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X-ray for Analytical Purposes

• X-ray for Analytical Purposes generated by
• 1. bombardment of metal target by a beam of high
  energy electrons
• 2. exposure of a substance to a primary beam of
  X-rays in order to generate a secondary beam of
  fluorencent X-rays
• 3. radioactive source whose decay process results
  in X-ray emission
• 4. from a synchrotron radiation source

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X-ray for Analytical Purposes

• "Distribution of continuous radiation from an
  X-ray tube with a tungsten target. The numbers
  above the curves indicate the accelerating
  voltages."

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X-ray for Analytical Purposes

• "Line spectrum for a tube with a molybdenum
  target."

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X-ray for Analytical Purposes

• Short wavelength limit of continuum function of
  accelerating voltage, not metal
• lo 12,398/V
• where V / volts, lo / A

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X-ray for Analytical Purposes

• 2 series of lines for all metals z gt 23 K L
  series
• 1 series of lines for all metals z lt 23 K series
• line spectrum min accelerating V to produce
  increases with Z

Mv
2 2 5/2
MIV
2 2 3/2
MIII
2 1 3/2
MII
2 1 1/2
MI
2 0 1/2
LIII
2 1 3/2
LII
2 1 1/2
LI
2 0 1/2
L series
K
1 0 1/2
K series
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X-Ray Fluorescence Spectroscopy
Mv
2 2 5/2
MIV
2 2 3/2
MIII
2 1 3/2
MII
2 1 1/2
MI
2 0 1/2
LIII
2 1 3/2
LII
2 1 1/2
Fluorescence
LI
2 0 1/2
hn
K
1 0 1/2
Qualitative analysis fluorescence lines reflect
intrinsic properties
of the atoms of interest. Quantitative
analysis non-destructive method.
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X-Ray Spectroscopy

• Emission (fluorescence)
• Absorption
• Diffraction

Beers law
Thickness of the sample
Linear absorption coefficient
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Diffraction of X-Rays

• Bragg's Law
• when AP PC nl scattered radiation
  will be "in phase"
• AP PC d sin q
• n l 2 d sin q

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Diffraction of X-Rays

• Bragg's Law "Diffraction of X-rays by a crystal."

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Diffraction

• Powder Pattern
• qualitative analysis gt ASTM database
• isostructural

American Society for Testing and Materials
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Zinc Blende CdSe !
111
220
331
531
422
311
400
511
440
620
20
60
40
100
80
120
2q (degree)
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Instrument Components

• Five basic components
• 1. source
• 2. device for restricting wavelength range
• 3. sample holder
• 4. radiation detector
• 5. signal processor and readout

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Sources

• "Schematic of an X-ray tube."

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Monochromator

• Device for restricting wavelength range
• filter gt thin metal, element to the left in the
  Periodic Table
• collimators slits

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X-ray Monochromator

• An X-ray monochromator and detector. Note the
  angle of the detector with respect to the beam
  (2Q) is twice that of the crystal face. For
  absorption analysis, the source is an X-ray tube,
  and the sample is located in the beam as shown.
  For emission work, the sample becomes a
  fluorescent source of X-rays as shown in the
  inset.

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Sample Holder

• - as crystal moves q, detector moves 2q
• - goniometer head for single crystal
• - cup for powder sample

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Goniometer Head for Single Crystal
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Radiation Detector

• X-ray film
• now used mainly for unit cell dimension and
  space group determinations
• Precession camera
• Weissenburg

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Weissenburg
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Radiation Detector

• Electrical Detectors
• 1. gas filled detectors
• gas is ionized by X-rays, conducts
• 2. scintillation counters
• X-rays strike phosphrs which give off light
• originally gt counted flasks
• now gt photomultiplier tube used to detect light

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Radiation Detector

• Electrical Detectors
• 3. semiconductor detectors
• lithium drifted silicon detectors
• charge-coupled device (CCD)

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Signal processor Readout devices

• high speed computer