X-Ray Spectroscopy.pptx

• INTRODUCTION
• GENERATION OF X-RAYS
• X-RAY TECHNIQUES
• PRINCIPLE
• INSTRUMENTATION
• APPLICATIONS
• CONCLUSIONS
• ACHIEVEMENTS
• REFERENCES
CONTENTS

INTRODUCTION:
• X-rays are discovered by Wilhelm Roentgen who
called them x-rays because the nature at first was
unknown so, x-rays are also called Roentgen rays.
• X-ray diffraction was discovered by Max.
•The wavelength range is 10-7 to about 10-15 m.
3

The penetrating power of x-rays depends on
energy also, there are two types of x-rays.
i) Hard x-rays: which have high frequency
and have more energy.
ii) soft x-rays: which have less penetrating
and have low energy

• X-ray spectroscopy is based on the
measurement of emission, absorption,
scattering, fluorescence and diffraction of
electromagnetic radiation.
• X-ray fluorescence and X-ray absorption
widely used for qualitative determination.

X-RAYS
1.X-rays are short wave length electromagnetic
radiations produced by the deceleration of
high energy electrons or by electronic
transitions of electrons in the inner orbital of
atoms
2.X-ray region 0.1to100 A˚
3.Analytical purpose 0.7 to 2 A˚ (0.1-25)
6

GENERATION OF X-RAYS
 By bombarding matter by High energy electrons
 X-ray photons (secondary beam of X-Ray fluorescence)
 By use of radioactive source
 From synchrotron radiation
 Cornell-high-energy synchrotron radiation laboratory
 Stanford synchrotron radiation laboratory
 Brookhaven national laboratory
7

Source of X-rays as
vacancy filled by
cascade of
electrons from
lower energy levels
8

Tube Spectrum
X-ray sources often
produce both continuous
and discontinuous (line)
spectra.
Both are of use in
analysis.
Bremsstrahlung
Characteristic
Spectrum
(target dependent)
lmin
12

Continum results from collision between electrons of the beam and atoms of target metal.
At each collision, electron is decelerated and aphoton of X-ray is produced.
Energy is equal to the difference in kinetic energy of electron before and after.
Max. X-ray energy = Max. electron energy
0
0
4
.
12
l
l 

 V
eV
hc

X-RAY TECHNIQUES
X-RAY FLOURESCENCE METHOD
X-RAY DIFFRACTION METHOD
X-RAY ABSORPTION METHOD
14

• X-ray fluorescence spectrometry relies on characteristic secondary
radiation emitted by materials when excited by a high-energy x-ray
source and is used primarily to determine amounts of particular
elements in materials.
• X-ray crystallography relies on the dual wave/particle nature of x-
rays to discover information about the structure of crystalline
materials.
• X-ray radiography is used for creating images of light-opaque
materials relies on the relationship between density of materials
and absorption of x-rays. Applications include a variety of medical
and industrial applications.

X-Ray Fluorescences
• The absorption of X-rays produces
electronically excited ions that return to their
ground state by transitions involving electrons
from highier energy levels.

Max Theodor Felix von Laue (9 October 1879 – 24 April 1960) was
a German physicist who won the Nobel Prize in Physics in 1914 for his
discovery of the diffraction of X-rays by crystals.
18

Diffraction of X-Rays
• The electric vector of the radiation interacts with
the electrons in the atoms of the matter to
produce scattering.
• When X-rays are scattered by the ordered
environment in a crystal, constructive and
destructive interference occurs among the
scattered rays because the distance between the
scattering centers are of the same order of
magnitude as the wave length of the radiation.
• Diffraction results.

PRINCIPLE
X-ray diffraction is based on constructive
interference of monochromatic x-rays and a
crystalline sample. These x-rays are generated by a
cathode ray tube, filtered to produce monochromatic
radiation ,collimated to concentrate and directed
towards the sample. The interaction of incident rays
with the sample produces constructive interference
when conditions satisfy Bragg’s law.
20

Bragg’s law
• When an X-ray beam strikes a crystal surface at
some angel θ.
• Part of the beam is scattered by the layer of
atoms at the surface.
• The unscattered part of the beam penetrates to
the second layer of the atoms where again a
fraction is scattered.
• The remainder passes on to the third layer and so
on.
• Cumulative effect of the scattering results
diffraction.

The requirements for diffraction are
• Spacing between layers of atoms must be roughly
the same as the wave length of the radiation
• The scattering centers must be spatially
distributed in a highly regular way.
• In 1912, W. L. Bragg treated the diffraction of X-
rays by crystal.
• A narrow beam of radiation strikes the crystal
surface at angle θ.
• Scattering results as a result of interaction of
radiation with atom located at O, P and R.

BRAGG’s EQUATION
William Henry Bragg
1862 – 1942
Nobel Prize in Physics
1915

d




 The path difference between ray 1 and ray 2 = 2d Sin
 For constructive interference: nl = 2d Sin
Ray 1
Ray 2

Deviation = 2
24
A
B
O
P
R
C
D

• If AP+PC=nλ
• Where n is an integer,
• The scattered radiation will be in phase at OCD,
and the crystal will appear to reflect the X-
radiation.
• But AP=PC=d sinθ
• Where d is the interplaner distance of the crystal.
• Thus, the conditions for consructive interference
of the beam at angle θ are nλ=2d sinθ.
• X-rays appear to be reflected from the crystal
only if the angle of incidence satisfies the
condition sinθ= nλ/2d.
• At other angles, destructive interference occurs.

“Constructive interference of the reflected beams emerging
from two different planes will take place if the path
lengths of two rays is equal to whole number of
wavelengths”.
for constructive interference,
nλ=2dsinФ
this is called as BRAGG’S LAW
26

The Bragg Equation
where n is an integer
l is the wavelength of the x-rays
d is the interplanar spacing in the specimen
 is the diffraction angle (discussed later!)
The Bragg equation is the fundamental equation, valid only for
monochromatic X-rays, that is used to calculate interplanar spacings
used in XRD analysis.

l sin
2d
n 

Diffractometer Components and Geometry

Our Scintag Diffractometer (Pt. 1)

Scintag Diffractometer Geometry

Spellman DF 3 Solid State High-voltage generator power supply
Scintag Diffractometer HV Power Supply

Bicron Scintillation Detector and Monochromator
Scintag Diffractometer Detector

From right to left:
Power module
Bias Power
Supply
Signal Amplifier
Ratemeter
(counter)
Scintag Diffractometer Detector Power Supply

Instrument components
• Absorption, emission, fluorescence and
diffraction of X-rays.
• Instruments for these application contain
components that are analogous in function to
the five components of instruments for optical
spectroscopicmeasurements.

• A source
• A device for restricting the wavelength range of incident radiation
• A sample holder
• A radiation detector/ transducer
• A signal processor and readout
• Components differ considerably in detail from the corresponding optical
components.
• However functions are the same.
• The ways they combine to form instruments are often similar to optical
spectrophotometer.
• First using filter
• Second using monochromator- to transmit desired wavelength
• In addition a third method is available for obtaining information about
isolated portions of an X-ray spectrum.
• Isolation is achieved by electronically with devices that discriminate
among various parts of a spectrum based on energy rather than
wavelength of radiation

• Thus,
• X-ray instruments are often described as
wavelength-dispersive instruments
• Or energy-dispersive instruments depending
on the method which the resolve the spectra.

INSTRUMENTATION
• Production of x-rays
• Collimator
• Monochromator
a.Filter
b.Crystal monochromator
• Detectors
a.Photographic methods
b.Counter methods
i. Geiger muller tube counter
ii. Proportional counter
iii. Scintillation counter
iv. Solid state semi-conductor detector
v. Semi-conductor detectors
37

PRODUCTIONOF X-RAYS:
 X-rays are generated when high velocity electrons
impinge on a metal target.
 Approximately 1% of the total energy of the electron
beam is converted into x-radiation.
 The remainder being dissipated as heat.
 Many types of x-ray tubes are available which are used
for producing x-rays.
39

Source
• Tubes (coolidge tube)
• Radio isotopes
• Secondary fluorescences

X-ray tube
 Filament (Tungsten)
 Target metal (Cu, Cr)
 Electrons are
accelerated by a
potential of about
55,000 Volts
 Typical wavelengths used
for X-ray experiments lie
between 0.6 and 1.9Å.
X-ray Tube
41

X-rays are generated by
directing an electron beam
on to a cooled metal
target. Beryllium is
transparent to X-rays (on
account of the small
number of electrons in
each atom) and is used for
the windows.
X-ray Tube (Continue)
42

X-ray production at instrumental level
16

Coolidge tube
•It consists of a Cathode which is a filament of tungsten metal heated by a battery
B to emit the thermoionic electrons.
•This beam of electrons constitutes the cathode ray stream.
•The anode consists of a heavy block of copper with a metal target plated on or
embedded in the surface of copper.
•The target metals as tungsten, chromium, copper, molybdenum, rhodium
scandium, silver, iron and cobalt
•If a positive voltage in the form of an anode(target) is kept near these electrons,
•the electrons are accelerated towards anode.
•On striking the anode, electrons transfer their energy to its metallic surface which
then gives off X-rays .
15

Radio isotopes
55Fe26, 57Co27, 109Cd48, 125I53, 147Pb82
Secondary fluorescent sources: X-rays with a
tungsten target could be used to excite the kα and Kβ lines
of molybdenum.

X-ray monochromators
• Consists of a pair of beam collimators, which
serve the same purpose as the slits in an
optical instrument and a dispersing element
mounted on a gonimeter or rotatable table.
• Permits variation and precise determination of
angle between crystal face and the collimated
incident beam.
• According to bragg’s law wave lengths are
diffracted.

COLLIMATOR:
 In order to get a narrow beam of x-rays, the x-rays
generated by the target material are allowed to pass
through a collimator which consists of two sets of
closely packed metal plates separated by a small gap.
 The collimator absorbs all the x-rays except the
narrow beam that passes between the gap.
47

TYPES OF MONOCHROMATORS
In order to do monochromatization,2 methods are
available
1.Filter
2.Crystal monochromator
a)Flat crystal monochromator
b)Curved crystal monochromator
Materials used-Nacl,LiF,quartz etc,.
48

DETECTORS
• The x-ray intensities can be measured and recorded
either by photographic or counter methods.
• Both these types of methods depends upon ability of
x-rays to ionize matter and differ only in the
subsequent fate of electrons produced by the ionizing
process.
49

DETECTORS
 Photographic methods
D=logIo/I
 Counter methods
a) Geiger-muller tube counter
b) Proportional counter
c) Scintillation detector
d) Solid-state semi-conductor detector
e) Semi conductor detectors:si(Li) &Ge(Li)
50

A) photographic method:
• In order to record position and intensity of x-ray beam a
plane cylindrical film is used.
• The film after exposing to x-rays is developed,the
blackening of the developed field is expressed in terms of
density units D given by
D=logIo/I
• D is related to the total x-ray energy that causes the
blackening of the photographic film and measured by
densitometer.
• .
51

B) Counter methods:
These are of many types, like
a. Geiger-muller tube counter
b. Proportional counter
c. Scintillation counter
d. Solid-state semiconductor detector
e. Semiconductor detector
52

a) Geiger-muller tube counter
• Filled with inert gases like argon.
• Positive potential of 800-2500 Volts
ADVANTAGES:
inexpensive,trouble free
detector,higher signal.
DISADVANTAGES:
used only for counting low
rates,efficiency falls off rapidly at
λ<1A°,cannot be used to measure
energy of ionising radiation.
53

b) Proportional counter:
 Construction is similar to Geiger-tube counter only
but proportional counter is filled with a heavier gas
like xenon or krypton.
 Heavier gas is preferred because it is easily ionised.
54

c) Scintillation counter
• In this detector, there is a large sodium iodide crystal activated
with a small amount of thallium.
• When x-rays incident upon crystal, the pulses of visible light
are emitted which can be detected by photomultiplier tube.
55

d)Solid state semi-conductor detector
• The electrons produced by X-ray beam are promoted
into conduction bands and the current which flows is
directly proportional to the incident X-ray energy.
Disadvantage:
• Mainted at very low Temp to minimise the noise and
prevent deterioration of the detector.
57

e) Semi-conductor detectors
 When x-ray falls on a semiconductor or a silicon lithium-
drifted detector,it generates an electron(-e) and a hole(+e) in a
fashion analogous to the formation of a primary ion pair in a
proportional counter.
 The principle is similar to that of gas ionization detector as
used in a proportional counter, except that the materials used
are in a solid state.
58

X-RAY DIFFRACTION METHODS
These are generally used for investigating the internal
structures and crystal structures of various solid
compounds.
They are
1.Laue’s photographic method
a)Transmission method
b)Back reflection method
2.Bragg’s X-ray spectrometer method
3.Rotating crystal method
4.Powder method
59

b)Back-reflection method
• This method is similar to Transmission method.
• However, black-reflection is the only method for the study of
large and thick specimens.
 Disadvantage:
• Big crystals are required
61

2)Bragg’s x-ray spectrometer method:
This method is based on Bragg’s law, bragg analysed the structures of
Nacl,KaI and ZnS.
62

APPLICATIONS
1. Structure of crystals
2. Polymer characterisation
3. State of anneal in metals
4. Particle size
determination
a) Spot counting method
b) Broadening of diffraction
lines
c) Low-angle scattering
5.Applications of diffraction
methods to complexes
a) Determination of cis-trans
isomerism
b) Determination of linkage
isomerism
6.Miscellaneous applications
65

1.STRUCTURE OF CRYSTALS
a-x-ray pattern of salt Nacl
b-x-ray pattern of salt Kcl
c-x-ray pattern of mixture of
Nacl &Kcl
d-x-ray pattern of a powder
mixed crystal of Nacl & Kcl
66

2.POLYMER CHARACTERISATION
• Determine degree of crystanillity
• Non-crystalline portion scatters x-ray beam to
give a continuous background(amorphous
materials)
• Crystalline portion causes diffraction lines that
are not continuous.(crystalline materials)
67

3.State of anneal in metals:XRD is used to to test the
metals without removing the part from its position and
without weakening it.
4.PARTICLE SIZE DETERMINATION
Spot counting method:
v=V.δθ.cosθ/2n
V=volume of individual crystallite
V=total volume irradiated
n=no. of spots in diffraction ring
δθ =divergence of x-ray beam
68

APPLICATIONS OF DIFFRACTION METHODS TO
COMPLEXES
a)Determination of
cis-Trans Isomerism:
Bis(pyridine-2-carboxamido)nickle(II)
chloride
b)Determination of linkage
isomerism:
Biuret+copper(II)=
pottassiumbis(biureto)
cuprate(II)tetrahydrate
69

MISCELLANEOUS APPLICATIONS
• Soil classification based on crystallinity
• Analysis of industrial dusts
• Assessment of weathering & degradation of minerals
& polymers
• Study of corrosion products
• Examination of tooth enamel & dentine
• Examination of bone state & tissue state
• Structure of DNA&RNA
70

CONCLUSIONS
 For materials including metals, minerals,
plastics, pharmaceuticals and
semiconductors XRD apparatus provide
highly accurate tools for non-destructive
analysis.
 The diffraction systems are also
supported by an extensive range of
application software
71

X-ray diffraction pattern for a single alum crystal.
Image by Dr H. J. Milledge, Department of Geology,
University College, London

X-ray diffraction image of a crystal of lysozyme
73

θ - 2θ Scan
The θ - 2θ scan maintains these angles with the
sample, detector and X-ray source
Normal to surface
Only planes of atoms that share this normal will be seen in the θ - 2θ Scan
76

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
77

X-ray diffraction by a single crystal
78

This is the principle behind X-ray diffraction (XRD) in
which an X-ray of known wavelength is focussed onto a
crystal that can be aligned until a diffraction pattern is
created. A blanker on the optical access blocks the
transmitted wavelengths.
79

An XRD pattern of silicon crystal
80

If multiple minicrystals are diffracted the resultant pattern will be a set of distinct
concentric rings, not discreet spots.
82

Formation of a powder pattern
83

A powder pattern of a crystalline is its “fingerprint”
84

Smaller Crystals Produce Broader XRD Peaks

/2 Example
• Polycrystalline sample has a number of peaks due to
mixture of crystal orientations.
10 20 30 40 50 60 70 80 90 100
0
2000
4000
6000
Polycrystalline Silicon Powder
Intensity
(counts/sec)
2
88

Diffraction Pattern
• Diffraction
patterns are a plot
of intensity vs 
89

Analytical applications of PXRD
• Identification of unknowns.
• Phase purity.
• Determination of lattice parameters.
• Determination of crystalline size.
• Quantitative Analysis
• Structure determination and refinement.
• Residual stress
• Texture analysis
90

Analytica Chimica Acta 538 (2005) 291–296
91

Bruker's X-ray Diffraction D8-Discover instrument

 1895 W.C. Roentgen discoversed X-rays (Nobel Prize 1901)
1910 Max von Laue: Diffraction Theory (Nobel Prize: 1912)
1915 W.L. Bragg & W.H. Bragg: NaCl, KCl (Nobel Prize Physics)2 • d • sin Θ = n • λ
1934 D. Bernal & D. Crowfoot examine first Proteins
1950 DNA double helix structure: Watson, Crick, Wilkins (Nobel Prize 1963)
1958 Myoglobin Structure (Nobel Prize 1962 Kendrew, Perutz)
1971 Insulin (Blundell)
1978 First Virus Structure (S.C Harrison)
1988 Nobel Prize: Photosynthetic reaction center (Huber, Michel, Deisenhofer)
1997 Nobel Prize: ATP-synthase structure (Walker)
1997 Nucleosome core particle (T. Richmond)
1999 Ribosome Structures (Steitz, …)
2000 Reovirus core structure (S.C. Harrison)
2000 Rhodopsin structure, GPCR (Palczewski et al.)
2002 ABC-Transporter (D. Rees et al.)
2003 R.MacKinnon: structures of ion channel (Nobel Prize Chemistry 2003)
X-Ray diffraction achievements
48

REFERENCES
1)Instrumental methods of chemical analysis ,B.K.sharma,17th
edition 1997-1998,GOEL publishing house.page no:329-359
2)Principles of instrumental analysis,5th edition ,by Dougles
a.skoog,f.James holles,Timothy A.Niemen.page no:277-298
3)Instrumental methods of chemical analysis ,Gurudeep
R.chatwal,sham k.anand,Himalaya publications page no:2.303-
2.332
4) Instrumental Methods Of Chemical Analysis –
H. Kaur pg.no:727-729,737
5) http://www.scienceiscool.org/solids/intro.html
6) http://en.wikipedia.org/wiki/X-ray_crystallography
94

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