Radioactive Decay and Decay Diagrams

Introduction

• This lecture discusses radioactive decay, focusing on specific decay processes and the various particles that can be emitted from nuclei.
• Generalized decay diagrams are used to represent various decay processes.

Generalized Decay Diagrams

• Axes on Decay Diagrams:
  • Energy (Y-axis): Increasing energy.
  • Atomic Number Z (Y-axis): Increasing atomic number.
• Diagrams are used to interpret decay processes like in uranium-235.

Types of Decay

Alpha Decay

• Involves emission of an alpha particle (helium nucleus: 4 mass number, 2 protons).
• Change: Parent nucleus (Z, A) to daughter nucleus (Z-2, A-4).
• Diagram: Moves left (decreasing Z and energy).

Beta Decay

• Involves emission of a beta particle (electron) and anti-neutrino.
• Change: Parent nucleus (Z, A) to daughter nucleus (Z+1, A).
• Diagram: Moves right (increasing Z).

Electron Capture

• Nucleus captures an electron; proton is neutralized.
• Change: Parent nucleus (Z, A) to daughter nucleus (Z-1, A).
• Diagram: Moves left (decreasing Z).

Positron Emission

• Emission of a positron (anti-electron), similar to beta decay but with opposite charge.
• Change: Parent nucleus (Z, A) to daughter nucleus (Z-1, A).
• Requires sufficient energy.

Neutron Emission

• Emission of a neutron from very unstable nuclei.
• Change: Parent nucleus (Z, A) to daughter nucleus (Z, A-1).
• Diagram: Moves straight down (decreasing mass number).

Gamma Decay

• Emission of a gamma photon, no change in Z or A but lower energy state.

Stability of Isotopes

• Even-Even vs. Odd-Odd Nuclei: Even-even are more stable.
• Example: Potassium-40 can decay through various mechanisms except alpha decay.

Decay Energy and Q Value

• Q Equation: Used to determine energy distribution among decay products.
• Alpha particle energy: Q value distributed between alpha and recoil nucleus.

Specific Decay Examples

• Carbon-14: Used in carbon dating, decays via beta decay.
• Molybdenum-99: Decays to technetium-99 metastable, used in medical imaging.
• Cobalt-60: Used in imaging, emits characteristic gamma rays.

Neutrino Detection

• Cherenkov Radiation: Detected in large water tanks, indicates neutrino interactions.

Positron Annihilation Spectroscopy

• Uses positrons to probe materials, detecting gamma rays from positron-electron annihilation.
• Helps measure atomic defects and material properties.

Safety and Biological Effects

• Most Dangerous Decay Types: Depends on exposure type (ingestion vs. external).
• Alpha Particles: Hazardous if ingested.
• Neutrons: Hazardous externally due to strong interaction.