(455) Alpha, beta, gamma decay [IB Physics SL/HL]

Alpha Decay

• Definition: A type of radioactive decay where an unstable nucleus emits an alpha particle (helium-4 atom).

• Ionizing Power: Alpha particles have high mass and are highly ionizing, causing significant damage to material (including biological tissues).

• Historical Context: Initially not well understood; the term "alpha" was a placeholder until further research provided clarity.

• Example Reaction: Uranium-238 undergoes alpha decay to form thorium and an alpha particle.

  • Atomic Number: 92 (Uranium) → 90 (Thorium) + 2 (alpha particle)

  • Mass Number: 238 → 234

Beta Decay

• Definition: Another form of radioactive decay where a beta particle is emitted from an unstable nucleus.

• Types of Beta Decay:

  • Beta Minus (Electron): An electron is emitted and a neutrino is produced.

    • Atomic bombardment can create a neutron, which decays into a proton, increasing atomic number.

  • Beta Plus (Positron): An antiparticle of an electron is emitted.

    • Positron is essentially a positively charged electron.

• Example of Electron Beta Decay: Cesium-137 undergoes electron beta decay to become barium-137 plus an electron and an anti-neutrino.

  • Atomic Number: 55 (Cesium) → 56 (Barium) - 1 (electron)

Gamma Decay

• Definition: A decay process where an element releases a gamma photon, a type of electromagnetic radiation.

• Characteristics: Does not change the atomic number or mass number of an element; simply indicates energy loss.

• Relevance: Less interesting because gamma decay does not transform the element itself; often a result of other decay processes or energy transitions.

Isotopes

• Definition: Different forms of the same element that have the same number of protons but different mass numbers (different numbers of neutrons).

• Example: Carbon-12 vs. Carbon-14; both are carbon, but Carbon-14 has more neutrons than Carbon-12.