Physics · MU Sofia

36. X-ray

Explains how X-rays are produced in a tube, from thermionic emission at the cathode and electron acceleration onto a metal target, then covers bremsstrahlung and characteristic radiation. It describes the intensity equation with its dependence on tube current, voltage and target atomic number, and the combined continuous and peaked spectrum. It closes with properties such as penetration and wavelength, and with applications in X-ray crystallography and X-ray luminescence.

Inside: 1 section · 3 labelled pictures · 10 flashcards · 2 min

Topic 37 of 42 in the MU Sofia syllabus for Physics (Dental Medicine, Year 1). The free AceMed note covers it in 1 section, about 351 words (2 min of reading), with 10 flashcards.

In this note

  1. Introduction

Introduction

Summary

  • The notes expand on the generation and characteristics of X-ray radiation, primarily produced in X-ray tubes through mechanisms like thermionic emission, followed by electron acceleration and collision with a metal target. They explore two primary X-ray production methods: Bremsstrahlung and characteristic radiation. The discussion extends to the intensity and spectrum of X-rays, detailing the factors influencing X-ray intensity and their spectral distribution. Additional insights into the properties of X-rays highlight their penetration capabilities and their role in applications such as X-ray crystallography and luminescence.

X-Ray (Roentgen Ray) Radiation and the Principle of Operation of X-Ray Tubes

  • Electron Production: Electrons are emitted from the cathode via thermionic emission when heated.
  • Acceleration and Collision: Electrons are accelerated towards the anode using high voltage, colliding with a tungsten target, where their kinetic energy is converted into X-ray radiation.
  • X-Ray Production: Through Bremsstrahlung and characteristic radiation, kinetic energy is transformed into X-rays.

Bremsstrahlung and Characteristic X-Ray Radiation

  • Bremsstrahlung Radiation: Produced when accelerated electrons are decelerated by the nuclei of the target atoms, emitting X-rays with a continuous spectrum.
  • Characteristic Radiation: Occurs when electrons displace inner-shell electrons of the target atom, causing outer-shell electrons to drop into the lower energy vacancies and emit X-ray photons characteristic of the target material.

Intensity and Spectrum of X-Rays

  • Intensity Equation: I(lambda) = k. Ia .U^2 .Z de scribing how the intensity depends on the tube current (I_a), voltage (U), and the atomic number (Z) of the target.
  • Spectrum: Combines the continuous spectrum of Bremsstrahlung with peaks from characteristic radiation, depicted graphically by the number of photons versus their energy or wavelength.

Properties of X-Rays

  • Energy and Penetration: High-energy photons with deep penetration capabilities, useful in medical imaging.
  • Wavelength: Shorter than visible light, enabling deep material penetration.
  • Absorption: Varies with X-ray type; soft X-rays are absorbed by air, while hard X-rays penetrate deeper into materials.

Applications in X-Ray Crystallography and Luminescence

  • X-Ray Crystallography: Essential for determining the structure of crystals by analyzing the diffraction patterns formed when X-rays are beamed at a crystalline sample.
  • X-Ray Luminescence: Analyzes material composition by inducing visible light emission in materials exposed to X-rays.

Read the full note free

The whole note is free with an AceMed account, with its 10 flashcards. Premium adds flashcard recall, highlights and Ask AI.

Start freeAlready a member? Open the note