X-rays are produced when high-energy electrons are suddenly decelerated or when their inner-shell interactions in atoms cause photon emission. In most practical applications, this happens inside an X-ray tube.
Here’s the step-by-step process:
- Electron Generation
- A heated filament (cathode) releases electrons via thermionic emission.
- This is similar to how an electric bulb filament glows and releases particles when heated.
- Acceleration of Electrons
- A high voltage (tens of thousands of volts, typically 30–150 kV in medical machines) is applied between the cathode (negative) and the anode (positive).
- This accelerates the electrons to very high speeds.
- Collision with Target Material
- The electrons strike a metal target on the anode (usually tungsten due to its high melting point and atomic number).
- X-ray Emission
- Bremsstrahlung radiation (“braking radiation”): When electrons slow down suddenly upon hitting the target, their lost kinetic energy is released as X-ray photons.
- Characteristic radiation: High-speed electrons knock out inner-shell electrons from the target atoms, and when outer electrons drop into the vacancy, energy is released as X-rays of specific wavelengths.
- Beam Direction and Filtering
- X-rays are directed through an opening in the tube housing.
- Filters may remove low-energy X-rays that would only increase patient dose without improving image quality.
- Shielding
- The rest of the tube is surrounded by lead shielding to prevent unnecessary radiation leakage.