Physics: X-Rays

X-Rays

• Electromagnetic radiation with very short wavelength (1-0.1 Å) and high penetrating power.
• Useful in diagnosis and radiotherapy.

Energy of X-Rays

• Energy of each photon depends on the frequency of radiation.
• Energy (E) = hυ = hc / λ, where h = Planck's constant (6.6 × 10⁻³⁴ J·s), c = velocity of light (3 × 10⁸ m/s), and υ = frequency of radiation.

X-Ray Production

• Produced when highly energetic electrons interact with matter, converting kinetic energy into electromagnetic radiation.
• Main components of an X-ray tube:
  • Source of electrons (cathode, filament), controlling the number of electrons and X-ray photons through tube current and time (mAs).
  • Evacuated space (glass envelope) for accelerating electrons.
  • High positive potential (kV) to control electron energy and X-ray photon energy.
  • Target (anode) for electrons to strike.

X-Ray Tube Efficiency

• Up to 99% of accelerated electron energy is converted to heat, while approximately 1% is converted to X-ray photons.
• Anode atomic number (Z) affects X-ray beam intensity, with higher Z (e.g., tungsten, Z = 74) producing more intense beams.

X-Rays

• X-rays are electromagnetic radiation (EMR) with a very short wavelength (λ 1-0.1 A°) and high penetrating power.
• They are useful in diagnosis and radiotherapy.

Energy of X-Rays

• The energy carried by each photon depends on the frequency of radiation: E = h υ = h c / λ.
• h is Planck's constant = 6.610−34 (joule.sec) and c is the velocity of light = 310^8 m/sec.

X-Ray Production

• X-rays are produced when highly energetic electrons interact with matter, converting kinetic energy into electromagnetic radiation.
• The main components of the X-ray tube are:
  • A source of electrons (cathode, filament)
  • An evacuated space to accelerate electrons
  • A high positive potential to control electron energy
  • A target for electrons to strike (anode)

X-Ray Tube Characteristics

• In the X-ray tube, up to 99% of accelerated electrons' energy is converted to heat, and approximately 1% is converted to X-ray photons.
• The higher the atomic number (Z) of the anode, the more intense the X-ray beam produced.
• Techniques to overcome overheating in the anode:
  • Use an anode material with a high melting point (e.g., tungsten at 3400 C°)
  • Equip the X-ray tube with two filaments for interchangeable focal spot sizes
  • Increase the area struck by electrons (focal spot area) without increasing image blurring by angulating the anode (line-focus principle)
  • Use a rotating anode X-ray tube (3600 rotations per minute)