Gamma rays penetrate materials because they have extremely high energy and very short wavelengths, which make them difficult to absorb. They don’t interact strongly with electrons compared to lower-energy photons, so they can travel long distances through solids before being absorbed or scattered.
1. How gamma rays penetrate materials
- Weak interaction with matter: They are uncharged photons, so they aren’t deflected by electric or magnetic fields.
- Main interactions:
- Photoelectric effect (dominates at low energies)
- Compton scattering (medium energies)
- Pair production (very high energies)
- Penetration depth: Can pass through several centimeters of lead or meters of concrete, depending on energy.
- Attenuation: The beam’s intensity decreases gradually as it passes through matter — thicker or denser materials reduce intensity more.
2. How this is used in imaging
Gamma-ray penetration is used in nuclear medicine and industrial radiography to create images based on how much radiation passes through an object.
Medical imaging (gamma cameras)
- Radioisotopes that emit gamma rays (e.g., Technetium-99m, Iodine-131) are introduced into the body.
- As they decay, gamma rays escape the body and are detected by gamma cameras.
- A computer reconstructs images showing organ structure and function (e.g., bone scans, heart imaging).
Industrial imaging (gamma radiography)
- A gamma-ray source (e.g., Cobalt-60, Iridium-192) is placed on one side of the object.
- A detector or photographic film is placed on the other side.
- Dense areas absorb more gamma rays and appear darker/lighter in the final image, revealing flaws like cracks, voids, or corrosion inside metal structures.
Advantages of gamma-ray imaging:
- Can image through thick, dense materials.
- Works without needing to disassemble equipment.
- In medicine, provides functional as well as structural information.