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SpectroscopIC aNALYSIS Part 7 – X-ray Analysis Methods. Chulalongkorn University, Bangkok, Thailand January 2012 Dr Ron Beckett Water Studies Centre & School of Chemistry Monash University, Melbourne, Australia Email: [email protected] Water Studies Centre. 1.

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slide1

SpectroscopIC aNALYSISPart 7 – X-ray Analysis Methods

Chulalongkorn University, Bangkok, Thailand January 2012

Dr Ron Beckett

Water Studies Centre & School of ChemistryMonash University, Melbourne, Australia

Email: [email protected]

Water

Studies

Centre

1

x ray analysis methods
X-ray Analysis Methods
  • Properties of X-radiation
  • X-ray diffraction
  • X-ray emission spectroscopy
  • Production of X-radiation in an X-ray tube
  • X-ray fluorscence

2

properties of x radiation
Properties of X-radiation
  • Frequency n3x1016 – 3x1018Hz
  • Wavelength l10 nm – 100 pm
  • High energy radiation, damaging to biological cells
  • High penetration of materials due to low absorbance is useful in medicine (body X-rays) and material science (fracture detection)

3

x ray diffraction by crystals
X-ray Diffraction by Crystals

X-rays are reflected from planes of atoms in the crystal lattice of compounds

6

x ray diffraction by crystals1
X-ray Diffraction by Crystals

X-rays reflected from two planes of atoms in the crystal lattice constructively interfere only when the path length difference is an integral number of wavelengths

7

For waves 1 and 2 path lengths BC + CD = l , 2 l , 3l , ...., n l

x ray diffraction by crystals2
X-ray Diffraction by Crystals

This condition results in the following law for X-ray diffraction by crystals

8

x ray powder diffraction patterns
X-ray Powder Diffraction Patterns

Direction of incident beam

Diffracted beams

9

Random orientation of crystals in the powder

slide14
X-ray Powder Diffraction Patternsare used to identify crystalline materials and to determine the amount of each phase in a mixture

14

single crystal x ray crystallography
Single Crystal X-ray Crystallography

Analysis of the geometry and intensity of spots enables the crystal and molecular structure of compounds to be determined

15

x ray studies lead to the discovery of the double helix structure of dna
X-ray Studies Lead to the Discovery of the Double Helix Structure of DNA

16

Rosalyn Franklin Single crystal X-ray pattern of DNA

x ray emission spectrometer
X-ray Emission Spectrometer

Monochrometer

Excitation Source

electrons

protons

X-rays

g-rays

19

x ray emission
X-ray Emission

Excitation Source

electrons

protons

X-rays

g-rays

X-ray Emission

x ray emission energy jumps
X-ray Emission Energy Jumps

Emission

Excitation

Emission

22

x ray emission spectroscopy
X-ray Emission Spectroscopy

X-ray emission spectrum of a Ni compound the exact position and intensity of the peaks can give information about the oxidation state and bonding

24

production of x radiation in an x ray tube
Production of X-radiation in an X-ray Tube

High voltage extracts electrons from the anode and accelerates them towards the metal cathode

These high energy collisions eject electrons from inner atomic orbitals of the metal

High Voltage ~100,000 V

_

+

e-

X-radiation

Frequency depends on target metal

Metal Target

production of x radiation in an x ray tube2
Production of X-radiation in an X-ray Tube

.

.

.

.

.

.

.

.

.

.

.

.

High energy electron after collision with metal atom in the target

High energy electron accelerated by voltage

e-

e-

e-

.

Inner shell electron ejected from the metal atom in the target

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.

.

.

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production of x radiation in an x ray tube3
Production of X-radiation in an X-ray Tube

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.

.

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EX-ray = hn = DEelectron

29

x ray fluorescence
X-ray Fluorescence

AtomicFluorescence

Excitation by X-rays ejects electrons from inner orbitals of atoms

Electrons from higher orbitals jump back to fill vacancies

Emission of fluorescence X-rays occurs

Results in Stokes shift to longer wavelength (lower energy since EFluorescence <EExcitation).

EExcitation = hnEx

e-

KE = 1/2mv2

EFluorescence = hnFl

e-

e-

30

x ray fluorescence instrument
X-ray Fluorescence Instrument

X-ray Excitation Source

Monochrometer

X-ray Tube

_

e-

+

Detector

EExcitation = hnEx

X-ray Emission

EFluorescence = hnFl

Sample

x ray fluorescence analysis
X-ray Fluorescence Analysis
  • The fluorescence frequencies can be used to identify the elements in the sample
  • The intensity of the fluorescent X-ray beam is used to determine the concentration of specific elements using callibration standards
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