Glossary Term

Term: Alpha Decay

Alpha decay is a type of radioactive decay where an atomic nucleus emits an alpha particle (helium-4 nucleus) and transforms into a different element.

Alpha Decay

Overview

Alpha decay is a type of radioactive decay where an atomic nucleus emits an alpha particle (helium-4 nucleus) and transforms into a different element. This process reduces the atomic number by 2 and the mass number by 4.

The Process

When a heavy nucleus undergoes alpha decay:

  • The nucleus emits an alpha particle (2 protons + 2 neutrons)
  • The remaining nucleus has 2 fewer protons and 2 fewer neutrons
  • The element changes to one that is 2 positions lower on the periodic table

Alpha Particle Properties

  • Composition: 2 protons + 2 neutrons (helium-4 nucleus)
  • Charge: +2 (due to 2 protons)
  • Mass: ~4 atomic mass units
  • Symbol: α or ⁴₂He

Penetration and Shielding

Alpha particles have limited penetrating power:

  • Range in air: ~2-10 cm
  • Stopped by: Paper, skin, clothing
  • Biological hazard: Dangerous if inhaled or ingested
  • External exposure: Generally not dangerous due to low penetration

Examples

Common alpha emitters:

  • Uranium-238 → Thorium-234 + α
  • Radium-226 → Radon-222 + α
  • Polonium-210 → Lead-206 + α

Applications

  • Smoke detectors: Americium-241 alpha source
  • Nuclear batteries: Plutonium-238 in space missions
  • Research: Alpha particle scattering experiments

Relevance to Nuclear Weapons

Alpha decay is important in nuclear weapons because:

  • Many fissile materials are alpha emitters
  • Alpha decay contributes to plutonium aging
  • Affects weapon reliability over time
  • Creates detection challenges due to limited penetration

Sources

Authoritative Sources:

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