X-ray Analysis Methods

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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
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
• Frequency n
3x1016 – 3x1018 Hz
• Wavelength l
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)
3
4
X-ray Imaging in Medicine and Dentistry
5
X-ray Diffraction by Crystals
X-rays are reflected from planes of atoms
in the crystal lattice of compounds
6
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
For waves 1 and 2 path lengths BC + CD = l , 2 l , 3l , ...., n7 l
X-ray Diffraction by Crystals
This condition results in the following law
for X-ray diffraction by crystals
8
X-ray Powder Diffraction Patterns
Direction of
incident beam
Diffracted beams
Random orientation of crystals in the powder
9
X-ray Powder Diffraction Camera
10
X-ray Powder
Diffraction Camera
11
X-ray Powder Diffractometer
12
X-ray Powder Diffractometer
13
X-ray Powder Diffraction Patterns
are used to identify crystalline
materials and to determine the amount
of each phase in a mixture
14
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
Rosalyn Franklin
16
Single crystal X-ray pattern of DNA
Single Crystal X-ray Diffraction
Monochrometers
17
Single Crystal X-ray Diffraction
Monochrometers
18
X-ray Emission Spectrometer
Excitation Source
electrons
protons
X-rays
g-rays
Monochrometer
19
X-ray Emission
Excitation Source
electrons
protons
X-rays
g-rays
X-ray Emission
20
X-ray Emission
21
X-ray Emission Energy Jumps
Excitation
Emission
Emission
22
X-ray Emission Energy Jumps
3d
3p
3s
2p
2s
1s
23
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
1. High voltage extracts electrons from the anode
and accelerates them towards the metal cathode
2. These high energy collisions eject electrons from
inner atomic orbitals of the metal
High Voltage ~100,000 V
+
Metal Target
e-
_
X-radiation
Frequency
depends on
target metal
25
Production of X-radiation in an X-ray Tube
26
X-ray Tube
27
Production of X-radiation in an X-ray Tube
High energy electron
accelerated by voltage
e-
..
.
..
.
e-
High energy electron
after collision with metal
atom in the target
e-
..
.
..
.
Inner shell electron
ejected from the metal
atom in the target
..
..
.
28
Production of X-radiation in an X-ray Tube
EX-ray = hn = DEelectron
..
..
.
.
.
..
.
29
X-ray Fluorescence
Atomic
Fluorescence
1.
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.
EExcitation = hnEx
eKE = 1/2mv2
e-
EFluorescence = hnFl
e-
Results in Stokes shift
to longer wavelength
(lower energy since
EFluorescence < EExcitation).
30
X-ray Fluorescence Instrument
X-ray Excitation Source
Monochrometer
X-ray Tube
+
e-
_
Detector
EExcitation = hnEx
X-ray Emission
EFluorescence = hnFl
Sample
31
X-ray Fluorescence Spectrometer
32
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
33
Thank You for your Attention !
34
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