UNIT -1

X-Ray Diffraction

BSc –III SEM. VI

Paper - XIV

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Mr. Mayur S. Ankalgi

“Dissemination of Education for Knowledge, Science and Culture”

-Shikshanmaharshi Dr. Bapuji Salunkhe

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Shri Swami Vivekanand Shikshan Sanstha’s

Raje Ramrao Mahavidyalaya, Jath

DEPARTMENT OF PHYSICS

Outline

• Introduction
• History
• How Diffraction Works
• Demonstration
• Analyzing Diffraction Patterns
• Applications
• Summary and Conclusions

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Introduction

Motivation:

• X-ray diffraction is used to obtain structural information about crystalline solids.
• Useful in biochemistry to solve the 3D structures of complex biomolecules.
• Bridge the gaps between physics, chemistry, and biology.

X-ray diffraction is important for:

• Solid-state physics
• Biophysics
• Medical physics
• Chemistry and Biochemistry

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X-ray Diffractometer

History of X-Ray Diffraction

1895 X-rays discovered by Roentgen

1914 First diffraction pattern of a crystal made by Knipping and von Laue

1915 Theory to determine crystal structure from diffraction pattern developed by Bragg.

1953 DNA structure solved by Watson and Crick

Now Diffraction improved by computer technology; methods used to determine atomic structures and in medical applications

The first X-ray

How Diffraction Works

• Wave Interacting with a Single Particle
• Incident beams scattered uniformly in all directions
• Wave Interacting with a Solid
• Scattered beams interfere constructively in some directions, producing diffracted beams
• Random arrangements cause beams to randomly interfere and no distinctive pattern is produced
• Crystalline Material
• Regular pattern of crystalline atoms produces regular diffraction pattern.
• Diffraction pattern gives information on crystal structure

NaCl

How Diffraction Works: Bragg’s Law

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nl=2dsin(Q)

• Similar principle to multiple slit experiments
• Constructive and destructive interference patterns depend on lattice spacing (d) and wavelength of radiation (l)
• By varying wavelength and observing diffraction patterns, information about lattice spacing is obtained

d

Q

Q

Q

X-rays of wavelength l

l

How Diffraction Works: Schematic

NaCl

How Diffraction Works: Schematic

http://mrsec.wisc.edu/edetc/modules/xray/X-raystm.pdf

NaCl

Demonstration

Array A versus Array B

• Dots in A are closer together than in B
• Diffraction pattern A has spots farther apart than pattern B

Array E

• Hexagonal arrangement

Array F

• Pattern created from the word “NANO” written repeatedly
• Any repeating arrangement produces a characteristic diffraction pattern

Array G versus Array H

• G represents one line of the chains of atoms of DNA (a single helix)
• H represents a double helix
• Distinct patterns for single and double helices

Credit: Exploring the Nanoworld

A

C

E

G

B

D

F

H

Analyzing Diffraction Patterns

• Data is taken from a full range of angles
• For simple crystal structures, diffraction patterns are easily recognizable
• Phase Problem
• Only intensities of diffracted beams are measured
• Phase info is lost and must be inferred from data
• For complicated structures, diffraction patterns at each angle can be used to produce a 3-D electron density map

Analyzing Diffraction Patterns

http://www.ecn.purdue.edu/WBG/Introduction/

d1=1.09 A

d2=1.54 A

nl=2dsin(Q)

Applications of X-Ray Diffraction

• Find structure to determine function of proteins
• Convenient three letter acronym: XRD
• Distinguish between different crystal structures with identical compositions
• Study crystal deformation and stress properties
• Study of rapid biological and chemical processes
• …and much more!

Summary and Conclusions

• X-ray diffraction is a technique for analyzing structures of biological molecules
• X-ray beam hits a crystal, scattering the beam in a manner characterized by the atomic structure
• Even complex structures can be analyzed by x-ray diffraction, such as DNA and proteins
• This will provide useful in the future for combining knowledge from physics, chemistry, and biology