Gamma rays interact with matter in a few key ways, depending on their energy and the type of material they pass through. Because they’re highly energetic and have no mass or charge, they penetrate deeply, but they can still lose energy through three main processes:
1. Photoelectric Effect
- A gamma-ray photon transfers all its energy to an electron in an atom, ejecting it.
- More likely at lower gamma-ray energies and in high atomic number materials (like lead).
- Important for radiation shielding.
2. Compton Scattering
- A gamma-ray photon collides with a loosely bound electron, transferring part of its energy and changing direction.
- This reduces the photon’s energy (longer wavelength) and produces a scattered photon plus an energetic electron.
- Dominates at medium energies.
3. Pair Production
- If the gamma-ray photon has energy greater than 1.022 MeV, it can transform into an electron–positron pair near a nucleus.
- The positron will eventually annihilate with an electron, producing two more gamma photons.
- Important at very high energies.
Effects of interaction:
- Ionization: Gamma rays indirectly ionize atoms through the energetic electrons they produce.
- Biological damage: Can break DNA strands, causing mutations or cell death.
- Attenuation: Materials like lead, concrete, or thick water layers reduce gamma-ray intensity by absorbing or scattering them.