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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: Ron.Beckett@monash.eduWaterStudiesCentre

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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

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Properties of X-radiation

• Frequency 3x1016 – 3x1018 Hz

• Wavelength 10 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)

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X-ray Imaging in Medicine and Dentistry

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X-ray Diffraction by Crystals

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

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X-ray Diffraction by CrystalsX-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

For waves 1 and 2 path lengths BC + CD = , ...., n 7

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X-ray Diffraction by Crystals

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

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X-ray Powder Diffraction PatternsDirection of incident beam

Random orientation of crystals in the powder

Diffracted beams

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X-ray Powder Diffraction Camera

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X-ray Powder Diffraction

Camera

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X-ray Powder Diffractometer

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X-ray Powder Diffractometer

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X-ray Powder Diffraction Patternsare used to identify crystalline materials and to determine the

amount of each phase in a mixture

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Single Crystal X-ray Crystallography

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

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X-ray Studies Lead to the Discovery of the Double Helix Structure of DNA

Rosalyn Franklin Single crystal X-ray pattern of DNA16

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Single Crystal X-ray Diffraction Monochrometers

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Single Crystal X-ray Diffraction Monochrometers

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X-ray Emission Spectrometer

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Excitation Source electrons protons X-rays -rays

Monochrometer

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X-ray Emission

Excitation Source electrons protons X-rays -rays

X-ray Emission

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X-ray Emission

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X-ray Emission Energy Jumps

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Excitation Emission Emission

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X-ray Emission Energy Jumps

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3d

3p3s

2p

2s

1s

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X-ray Emission Spectroscopy

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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

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Production of X-radiation in an X-ray Tube1. High voltage extracts electrons from the anode

and accelerates them towards the metal cathode2. These high energy collisions eject electrons from

inner atomic orbitals of the metal

_+ e-

Metal Target

High Voltage ~100,000 V

X-radiationFrequency depends on target metal

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Production of X-radiation in an X-ray Tube

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X-ray Tube

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Production of X-radiation in an X-ray Tube

e-

e-

e-

..

...

......

..

...

.High energy electron accelerated by voltage

High energy electron after collision with metal atom in the target

Inner shell electron ejected from the metal atom in the target

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Production of X-radiation in an X-ray Tube

.

...

......

EX-ray = hEelectron

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X-ray Fluorescence Atomic

Fluorescence1. Excitation by X-rays

ejects electrons from inner orbitals of atoms

2. Electrons from higher orbitals jump back to fill vacancies

3. Emission of fluorescence X-rays occurs

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

EExcitation = h e-

e-EFluorescence = h

KE = 1/2mv2

e-

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X-ray Fluorescence Instrument

_+ e-

EExcitation = h

Detector

EFluorescence = h

Sample

X-ray TubeMonochrometer

X-ray Excitation Source

X-ray Emission

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X-ray Fluorescence Spectrometer

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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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Thank You for your Attention !