MEVE 018: Unit 07 - Scattering and Diffraction

-

UNIT 7: SCATTERING AND DIFFRACTION

7.0 Introduction

Scattering and diffraction are fundamental physical processes that reveal the structure of matter. When X-rays interact with materials, they can be scattered or diffracted depending on the internal arrangement of atoms or molecules. These interactions form the basis of various powerful analytical techniques used in chemistry, materials science, and environmental science. This unit introduces the generation and properties of X-rays, types of scattering, principles of X-ray diffraction (XRD), and their applications in environmental monitoring.

7.1 Objectives

Upon completing this unit, learners will be able to:

  • Understand how X-rays are generated and their physical properties.
  • Differentiate between X-ray scattering and diffraction.
  • Apply Bragg’s Law to interpret diffraction patterns.
  • Describe various experimental methods of XRD.
  • Explore the environmental applications of scattering and diffraction techniques.

7.2 X-Rays: Generation and Properties

X-rays are a form of electromagnetic radiation with wavelengths ranging from 0.01 to 10 nanometers. They are produced when high-energy electrons strike a metal target (usually tungsten or copper) in an X-ray tube.

Properties of X-rays:

  • High energy and short wavelength
  • Penetrate most materials except very dense ones (like lead)
  • Cause ionization and can damage biological tissue
  • Can be diffracted and scattered by atomic-scale structures

X-rays are ideal for probing atomic and molecular arrangements due to their short wavelengths, which are comparable to interatomic distances.

7.3 X-ray Scattering

X-ray scattering occurs when X-rays encounter electrons and change direction. The nature of this interaction varies with the size and structure of the scattering material.

7.3.1 X-ray Scattering from an Electron

When an X-ray beam hits a free or loosely bound electron, it is scattered in various directions. This is called Thomson scattering.

  • The scattered intensity depends on the angle and energy of the incident X-rays.
  • Scattered waves interfere and provide information about electron density.

7.3.2 X-ray Scattering from an Atom

Atoms contain multiple electrons. X-rays scattered from different electrons interfere with one another, creating a pattern related to atomic arrangement.

  • The scattering factor increases with atomic number.
  • This atomic-level scattering contributes to overall diffraction patterns.

7.3.3 Small Angle X-ray Scattering (SAXS)

SAXS is a technique where X-rays are scattered at very small angles to study large structures like:

  • Polymers
  • Proteins
  • Colloids
  • Nanoparticles

SAXS helps in understanding size, shape, and aggregation behavior of environmental colloids and pollutants.

7.4 X-ray Diffraction

X-ray diffraction (XRD) occurs when X-rays are directed at a crystalline material, and they are scattered in specific directions that constructively interfere to form diffraction patterns.

XRD is a non-destructive technique widely used to study crystalline structure, phase identification, and crystal orientation.

7.4.1 Diffraction from a Crystal Lattice

Crystals are made of a regular array of atoms. When X-rays strike the lattice planes, they are reflected and interfere either constructively or destructively, depending on the path difference.

Constructive interference (i.e., diffraction) occurs when the path difference equals an integer multiple of the X-ray wavelength.

7.4.2 Bragg’s Law

The condition for diffraction is defined by Bragg’s Law:

nλ=2dsin⁡θn\lambda = 2d\sin\thetanλ=2dsinθ

Where:

  • nnn = order of diffraction (an integer)
  • λ\lambdaλ = X-ray wavelength
  • ddd = interplanar spacing
  • θ\thetaθ = angle of incidence/reflection

Bragg’s Law is used to calculate interatomic distances, identify crystal structures, and study mineral phases.

7.4.3 Experimental Methods of X-ray Diffraction

There are several XRD techniques used in laboratories:

  1. Powder X-ray Diffraction (PXRD):
    • Sample in powdered form
    • Measures diffraction pattern from random orientations
    • Used for phase identification and crystallinity
  2. Single-Crystal XRD:
    • Uses a well-defined crystal
    • Provides 3D information about molecular structure
  3. Grazing Incidence XRD (GIXRD):
    • Used for thin films and surfaces
  4. Synchrotron XRD:
    • High-intensity X-rays for advanced structural studies

7.5 Environmental Applications of Scattering and Diffraction

Scattering and diffraction techniques play a vital role in environmental chemistry and geochemistry:

  • Identification of mineral phases in soils and sediments
  • Characterization of pollutants such as heavy metal oxides or crystalline pesticides
  • Study of particulate matter from air and industrial emissions
  • Analysis of colloidal suspensions and nanoparticles in water using SAXS
  • Monitoring changes in soil structure due to contamination
  • Studying the fate of pollutants during treatment processes (e.g., crystallization in sludge)

These techniques are essential for environmental monitoring, remediation studies, and material characterization.

7.6 Summary

This unit introduced the principles and applications of X-ray scattering and diffraction, particularly in the context of environmental science. X-rays, due to their unique wavelength, interact with matter to produce patterns that reflect atomic arrangements. Bragg’s Law provides the theoretical foundation for interpreting these patterns. Techniques like XRD and SAXS are indispensable for understanding the physical and chemical properties of environmental samples, including soils, sediments, particulate matter, and pollutants.

Keywords

  • X-rays-High-energy electromagnetic radiation with wavelengths between 0.01–10 nm, used in material analysis.
  • Scattering-Deviation of X-rays from a straight trajectory due to interaction with electrons or atoms.
  • Diffraction-Constructive interference of scattered X-rays from crystal planes resulting in a pattern.
  • Bragg’s Law-Equation that defines the condition for constructive interference of diffracted rays: nλ=2dsinθ
  • SAXS (Small Angle X-ray Scattering)-Technique to study the structure of particles and macromolecules at nanometer scale.
  • XRD (X-ray Diffraction)-Analytical method for identifying and characterizing crystalline materials.
  • Electron Scattering-Scattering of X-rays by free or loosely bound electrons.
  • Powder XRD-A type of XRD where the sample is in powdered form for phase identification.

Comments

Post a Comment

Popular Posts

Jcert Class 8 Daffodil Chapter 1a: The Naive Friends Solutions

-
Chapter 1a : The Naive Friends Answer the following questions: 1. Which questions made Keshav and Shyama curious about the egg? Ans.         How did the chick come out? How big would the eggs? How many? What colours would they? What did they eat? Such types of questions made Keshav and Shyama curious about the egg. 2. What three things did the children do to protect the eggs? Ans.         The children done three things are: (i)          Adjustment of food. (ii)        Adjustment of water. (iii)      Adjustment of roof. 3. Why did Keshav think of making a cushion for the eggs? Ans.         When Keshav saw the egg on direct sun light, he thaught making a cushion for the eggs. 4. What excuse did Keshav give for not showing the eggs to Shyama? Ans.     ...
Read more

Jcert Class 8 भाषा मंजरी Chapter 3 मित्रता Solutions

-
अध्याय - 3 : मित्रता 1. आप किस प्रकार कह सकते हैं कि मित्रों के चुनाव की उपयुक्तता पर हमारे जीवन की सफलता निर्भर करती है? उ. मित्रों के चुनाव की उपयुक्तता पर हमारे जीवन की सफलता निर्भर करती है क्योंकि संगति का गुप्त प्रभाव हमारे आचरण पर पड़ता है और यदि हमें अच्छी संगति, अच्छे मित्र मिलते हैं तो वे हमें सफलता की ओर ले जाते हैं जबकि बुरी संगति हमारे जीवन को खाक में मिला देती है।  2. 'विश्वासपात्र मित्र जीवन की एक औषध है।' आशय स्पष्ट कीजिए। उ. 'विश्वासपात्र मित्र जीवन की एक औषध है'- ऐसा इसलिए कहा गया है कि यदि हमें विश्वासी मित्र मिल गया तो हम अपने जीवन में चाहे जैसा भी कदम उठाएँ, उस कदम की आलोचना करके वह हमें सही दिशा की ओर उन्मुख करेगा। हम अपनी गलती रूपी बीमारी को उसकी आलोचना रूपी औषधि से दूर कर सकेंगे।  3. मित्र का चुनाव करते समय हमें किन बातों का ध्यान रखना चाहिए? उ. मित्र का चुनाव करते समय हमें निम्नलिखित बातों का ध्यान रखना चाहिए हमारे अच्छे विचारों (संकल्पों) को दृढ़ करने वाला हो। हमें दोषों और त्रुटियों से बचाए। हमारे सत्य, पवित्रता ...
Read more

Jcert Class 8 भाषा मंजरी Chapter 8 अमरूद का पेड Solutions

-
अध्याय - 8 : अमरूद का पेड 1. लेखक को क्यों लगता है कि इन सब पिछड़े खयालातों का हमारे घर में गुजर नहीं हो सकेगा। उ. अमरूद के पेड़ को देखकर सबसे पहले बाबू कन्हैयालाल की बूढ़ी पत्नी ने एक दिन टोका कि पश्चिम की तरफ अगर मकान का मुखड़ा हो और सामने ही अमरूद का पेड़ तो 'राम-राम बड़ा अशुभ होता है और माँ के चेहरे पर थोड़ा-सा भय दिखा पर लेखक को विश्वास था कि इन सब पिछड़े खयालातों का हमारे घर में गुजर नहीं हो सकेगा क्योंकि उसके घर के लोग आधुनिक विचारधारा के थे उसकी माँ सत्याग्रह के दिनों में अजमेर में लम्बा जेल कर चुकी है। पिताजी खुद राजनैतिक सामाजिक उदारता वाले आदमी थे। बुआ ने विवाह नहीं किया था, पढ़ने-लिखने में ही अपनी सम्पूर्ण जिन्दगी लगा दी और समाज कोई चुनौती देने का साहस नहीं कर सका। साथ ही परिवार के सभी लोगों में पिछड़ेपन के प्रति भर्त्सना का भाव था। 2. अमरूद के पेड़ की छाया किस प्रकार लेखक को उनके भाई-बहनों के साथ जोड़ती है ? उ. अमरूद के पेड़ की छाया लेखक को उसके भाई-बहनों के साथ जोड़ती है। वे सभी अमरूद की छाया में बेंत की कुर्सियों पर बैठ चर्चाएँ करते थे जिससे उनके बीच...
Read more