Gamma Rays

What Are Gamma Rays?

Gamma rays are the highest-frequency, shortest-wavelength electromagnetic waves. They occupy the extreme upper end of the electromagnetic spectrum.

• Wavelength range: From about $10^{-10} \, \text{m}$ down to less than $10^{-14} \, \text{m}$.
• Frequency range: Correspondingly the highest — above about $3 \times 10^{18} \, \text{Hz}$ (since $c = f\lambda$).

Because of their extremely short wavelength and high energy, gamma rays are produced in the most energetic processes in nature.

How Are Gamma Rays Produced?

Gamma rays are produced in two main ways:

1. Nuclear reactions — during processes like nuclear fusion or fission.
2. Radioactive decay — when an unstable atomic nucleus emits excess energy in the form of gamma radiation.

In both cases, the source is the nucleus of an atom, not its electrons. This is a key distinction from X-rays (which come from electron transitions in inner shells).

Physical Properties and Interaction with Matter

• Gamma rays are highly penetrating — they can pass through many materials, including human tissue.
• They interact with matter primarily through:
  • Photoelectric effect
  • Compton scattering
  • Pair production (at very high energies)

Because of their high energy, they can ionize atoms (knock electrons out of their orbits), making them a form of ionizing radiation.

Applications in Medicine

The most important application mentioned in the textbook is cancer treatment:

• Gamma rays are directed at cancerous tumors to destroy cancer cells.
• This works because the high-energy radiation damages the DNA of rapidly dividing cells more than normal cells.

Key Distinction from Other EM Waves …