1. What are gamma rays?
Gamma rays are the highest-energy waves in the electromagnetic spectrum. They have extremely short wavelengths and very high frequencies, giving them enormous penetrating power. Because of their high energy, gamma rays can pass through most materials and can even penetrate several centimetres of lead.
Gamma rays are invisible to the human eye and are produced in very energetic processes, both on Earth and in outer space.
1.1. Position in the electromagnetic spectrum
Gamma rays lie above X-rays in the spectrum. Their wavelengths are shorter than about 0.01 nanometers, and their frequencies exceed \(10^{19} \, \text{Hz}\).
1.2. General characteristics
- Wavelength: less than 0.01 nm
- Frequency: greater than \(10^{19} \, \text{Hz}\)
- Extremely high penetrating power
- Highly energetic photons with ionising ability
2. How gamma rays are produced
Gamma rays are generated in processes involving very high energies, usually at the nuclear or subatomic level. They are produced by transitions within atomic nuclei, particle interactions, or extremely violent cosmic events.
2.1. Radioactive decay
Many unstable atomic nuclei release excess energy by emitting gamma rays. This type of radiation often accompanies alpha or beta decay.
2.2. Nuclear reactions
Gamma rays are produced during nuclear fission, fusion, and other nuclear transitions when excited nuclei drop to lower energy states.
2.3. Particle interactions
High-energy particle collisions, such as those in particle accelerators or during cosmic ray interactions, also produce gamma photons.
2.4. Cosmic sources
- Supernova explosions
- Neutron stars
- Black hole accretion disks
- Gamma-ray bursts (the most energetic known events)
3. Interaction of gamma rays with matter
Gamma rays interact with matter mainly through ionisation processes. Their extremely high energy makes them capable of penetrating deep into materials and living tissues.
3.1. Penetrating power
Gamma rays can travel through metals, concrete, and human tissue. Dense materials like lead or thick concrete are used to absorb or block them.
3.2. Ionisation effects
Gamma rays can remove electrons from atoms, creating ions. This makes them dangerous at high doses, as ionisation can damage cells and DNA.
3.3. Absorption and scattering
Gamma rays lose energy by interacting with electrons and nuclei inside matter. These processes include photoelectric effect, Compton scattering, and pair production.
4. Uses of gamma rays
Despite their high energy and potential hazards, gamma rays are extremely useful in medicine, industry, and scientific research.
4.1. Medical applications
- Cancer treatment (radiotherapy): Focused gamma rays kill cancer cells by damaging their DNA.
- Sterilisation: Gamma rays are used to sterilise medical equipment by killing microbes.
- Diagnostic imaging: Some medical scans use radioactive tracers that emit gamma rays.
4.2. Industrial applications
- Checking structural defects in metal parts
- Food irradiation to kill bacteria and pests
- Measuring thickness of materials
4.3. Scientific research
- Astronomy uses gamma-ray telescopes to observe violent cosmic events
- Particle physics experiments study gamma emissions from particle collisions
- Geology uses gamma radiation to analyze rock composition
5. Safety and hazards of gamma rays
Gamma rays can be dangerous even at relatively low doses because of their strong ionising ability. Proper shielding and controlled exposure are essential.
5.1. Harmful effects
- Cell and DNA damage
- Increased risk of cancer
- Radiation sickness at high exposures
- Organ damage if exposure is prolonged
5.2. Protective measures
- Using thick lead or concrete barriers
- Maintaining safe distances from gamma sources
- Limiting exposure time
- Wearing radiation badges in labs or hospitals
6. Example: Gamma rays in cancer therapy
In radiotherapy, a focused beam of gamma rays is directed at cancerous tissue. Because gamma rays can penetrate deep inside the body, they can deliver energy directly to the tumour. The strong ionising effect damages the DNA of cancer cells, slowing or stopping their growth. Care is taken to minimize exposure to healthy tissue.