Overview
This lecture explains the three primary types of radioactive decay—alpha, beta, and gamma decay—including their mechanisms, effects, and applications in medicine.
Alpha Decay
- Alpha decay is when a nucleus emits an alpha particle, made up of two protons and two neutrons (helium nucleus).
- The atom's mass number decreases by four, and its atomic number decreases by two.
- Alpha particles have low penetration power and can be stopped by paper or skin.
- Alpha radiation is only a significant health hazard if ingested or inhaled.
- Alpha particles cause damage by producing free radicals and lowering white blood cell count.
- Organs like the liver, kidneys, spleen, bone marrow, and gastrointestinal tract are especially vulnerable to alpha radiation.
Beta Decay
- Beta decay involves emission of high-energy electrons (beta particles) from the nucleus.
- Beta particles are smaller than alpha particles, can travel further, and have greater penetration but less ionizing power.
- Beta decay happens when the nucleus has too many protons or neutrons.
- Beta-plus decay: proton turns into a neutron, emitting a positron and a neutrino.
- Beta-minus decay: neutron turns into a proton, emitting an electron (beta-minus) and an electron antineutrino.
- Beta-minus decay is more common than beta-plus decay.
- Beta radioisotopes are used in cancer treatment (brachytherapy) and medical imaging (PET scans).
Gamma Decay
- Gamma decay releases a high-energy gamma-ray photon without ejecting particles from the nucleus.
- Gamma rays are electromagnetic radiation with high frequency and energy, invisible to humans.
- Gamma decay does not change the atom's composition or element.
- Gamma rays have high penetration and require thick lead or concrete for shielding.
- Used in medicine (gamma knife surgery) and for sterilizing food and equipment.
Summary and Comparisons
- Alpha decay: nucleus loses two protons, changing element.
- Beta decay: nucleus can lose or gain a proton, changing element.
- Gamma decay: no change in proton number, element remains the same.
- Radioactive decay can damage living tissue; alpha is least penetrating, gamma is most.
Key Terms & Definitions
- Alpha Particle — two protons and two neutrons; a helium nucleus.
- Beta Particle — a high-energy electron or positron emitted from a nucleus.
- Gamma Ray — high-energy electromagnetic radiation emitted from a nucleus.
- Positron — antimatter equivalent of an electron with a positive charge.
- Neutrino — uncharged, nearly massless particle emitted during beta decay.
Action Items / Next Steps
- Review the differences between alpha, beta, and gamma decay.
- Read about practical medical uses of radioactive isotopes.
- Prepare for questions on decay types and their biological effects.