UNDISTORTED SCIENCE II: Episode 3 - Radioactivity

Overview

• Common misconceptions about radioactivity (associated mainly with nuclear power plants and atomic bombs).
• Radioactivity is a natural part of the universe and vital for understanding our planet.

Discovery of Radioactivity

• Discovered by Henri Becquerel in 1896 in uranium salts.
• Defined as the property of substances to emit invisible radiation.
• A spontaneous process involving transformation of unstable atomic nuclei into lighter, more stable ones.

Stability of Nuclei

• Stability determined by the neutron-to-proton ratio:
  • Light nuclei: Stable isotopes have similar numbers of protons and neutrons.
  • Heavy nuclei: Stable isotopes have more neutrons than protons.
• Example: Carbon isotopes 12C (6 protons, 6 neutrons) and 13C (6 protons, 7 neutrons).

Isotopes and Radioactivity

• Isotopes: Variants of elements with the same number of protons but different numbers of neutrons.
• Carbon has two stable isotopes (12C, 13C); others are radioactive.
• All elements heavier than bismuth are radioactive.

Types of Radioactivity

1. Alpha Decay

   • Emission of alpha particles (helium nucleus).
   • Slow-moving, low penetration; blocked by paper or air.

2. Beta Decay

   • Emission of electrons or positrons.
   • Requires stronger shielding (thin metal sheets).

3. Gamma Radiation

   • High-frequency electromagnetic radiation (energetic photons).
   • Most penetrating; requires thick lead for shielding.

Natural Radioactivity Sources

• Two main sources:
  1. Radioactive Atoms from Stars
     • Long-lived isotopes found on Earth (e.g., U-235, U-238).
     • Regions with high radiation levels: Vysočina, Třebíč, parts of France, Italy, Kerala, Brazil, Nile Delta.
     • Thorium-232 also decays via alpha decay.
  2. Cosmic Radiation
     • High-energy hydrogen nuclei from space interacting with the atmosphere.
     • Produces radioactive isotopes like tritium and carbon-14.

Importance of Radioactive Isotopes

• Essential elements in living organisms include carbon-14 and potassium-40 (gamma emitter).
• Human bodies are naturally radioactive due to these isotopes.

Measuring Radiation

• Dosimeter: Device used to measure radiation intensity.
• Effective dose measured in sieverts (Sv).
  • Average annual dose in the Czech Republic: 0.0025 Sv (2.5 mSv).
  • Artificial sources contribute about one-fifth of the natural background dose.

Health Risks from Radiation

• Dosages affecting health: 0.050-0.200 Sv can have low probability risks over time; >1 Sv poses immediate risk of radiation sickness.
• Awareness of potential risks in environments like nuclear power or space travel.

Applications of Radioactivity

• Medical Uses: Diagnosis and therapy (especially for tumors).
• Agriculture: Kills pathogens (bacteria, fungi).
• Archaeology: Radiocarbon dating to determine age of substances.

Conclusion

• Radioactivity requires respect and understanding; not something to fear.
• Encouragement for further study in the field of radioactivity.