The document discusses X-ray diffraction, a non-destructive method of chemical analysis that produces unique diffraction patterns for crystalline substances, akin to a fingerprint. It highlights the principles of X-ray generation, methods of producing X-rays, and the advantages and disadvantages of X-ray techniques for studying atomic and molecular structures. Additionally, it covers specimen preparation and the significance of adherence to Bragg's law for constructive interference in diffraction observations.

1. Presented by :- Faraz Ahmad Khan
(M.Sc. 3rd Semester)
“ X - Ray Diffraction ”Presented to :-
Dr. Dinesh K. Yadav
& Dr. Rajiv K. Yadav

2. Introduction
• X-Ray diffraction is a method of X-Ray
Crystallography, in which a beam of X-rays strikes
a sample (crystalline solid), land on a piece of a
film or other detector to produce scattered
beams.
• It is novel & non destructive method of chemical
analysis and a variety of X-Ray techniques in
practice.
• These are: 1.) X-Ray Absorption; 2.) X-Ray
Diffraction; 3.) X-Ray Fluorescence

3. • “Every crystalline substance gives a pattern;
the same substance always gives the same
pattern; and in a mixture of substance each
produces its pattern independently of the
others.”
• The X-Ray diffraction pattern of a pure
substance is, therefore, like a fingerprint of
the substance. It is based on the scattering of
x-rays by crystals.
• It shows the arrangement of atoms with in a
crystal.

5. Electromagnetic Spectrum
10-1 to 10 nm
400 to 700 nm
10-4 to 10 -1 nm
10 to 400 nm
700 to 104 nm
X-ray radiation was discovered by
Roentgen in 1895.
X-rays are generated by bombarding
electrons on an metallic anode
Emitted X-ray has a characteristic
wavelength depending upon which metal is
present.
e.g. Wavelength of X-rays from Cu-anode
= 1.54178 Å
E= hn= h(c/l)
l(Å)= 12.398/E(keV)
NMR
10 um - 10 mm

6. Bragg Diffraction
d
q
q
d sinq
For constructive interference 2d sin q = l
d- Spacing between two atoms
q- Angle of incidence of X-ray
l- Wavelength of X-ray
•Diffraction occurs only when Bragg’s Law is satisfied, conditon for
constructive interference.

7. A protein crystal is placed in the x-ray beam
The x-rays are
diffracted by the
electron clouds
around atoms
The atomic structure
can be deduced from
the data

8. Specimen Preparation
• Powders :-
0.1 micro m < particle size < 40 micro m
(Peak broadining) (Less diffraction)
• Bulks:- Smooth surface after polishing, specimen
should be thermal annealed to eliminate any surface
deformation induced during polishing.

9. Production of X-Rays
• X-rays are produced whenever high speed
electrons collide with a metal target.
• A source of electrons-hot Tungsten filament, a
high accelerating voltage between the
cathode(W) and the anode and the metal
target Cu, Al, Mo, Mg.
• The anode is a water cooled block of Cu
containing desired target metal.

11. Two method of X-ray Generation
1.) Characteristic X-ray generation:-
• When a high energy electron
collides with an inner shell
electron both are ejected from
the tungsten atom leaving a
'hole' in the inner layer.
This is filled by an outer shell
electron with a loss of energy
emitted as an X-ray photon.

12. 2.) Bremsstrahlung /Braking X-ray generation
• When an electron passes near the nucleus it is
slowed and its path is deflected. Energy lost is
emitted as a bremsstrahlung X-ray photon.
• Bremsstrahlung = Braking radiation
• Approximately 80% of the population of X-rays
within the X-ray beam consists of X-rays generated in
this way.

13. 1- Photographic film
Not much used anymore because of the availability of far more
sensitive detectors. Superior resolution due to its fine grain, but
limited dynamic range.
2- Image plates
Image plates are coated with a layer of inorganic storage
phosphor. X-ray photons excite electrons in the material to
higher energy levels. Part of the energy is emitted as
fluorescence, but an appreciable amount of energy is retained in
the material. The stored energy is released upon illumination
with a red laser. Blue light is emitted and measured with a
photomultiplier. The light emitted is proportional to the number
of photons. Ten times more sensitive than film, dynamic range
(1:104-105)
Detectors
S. Doublié © 2000

15. X-Ray Scattering and observation
A typical image of x-rays
scattered by a crystal:
(Dark spots are the
scattered x-rays)
X-Ray Diffraction Pattern
M. Rould ‘02

16. Advantages :-
• To study Atomic and molecular structure of crystal, fast
method and easy sample preparation.
• Used to determine structure of protein and elucidate its
function.
• Distinguish between different materials with identical
composition on basis of shape, size and internal stress.
• It can determine the orientation of a crystal and non
destructive, highly accurate and reliable.
Disadvantages:-
• All X-rays may cause alteration of cellular division and
other intracellular processes and are therefore
potentially harmful to the human body.Damage Skin.

17. Referances
• Principles and Techniques of Biochemistry and
Molecular Biology by Wilson and Walker.
• Fundamentals and Techniques of Biophysics
and Molecular Biology by Pranav Kumar.