Ficha de revisão: Understanding Radioactivity and Nuclear Reactions

Unit 18: Radioactivity - Revision Sheet

1. 📌 Essentials

• Atom: smallest unit matter; consists of nucleus and electrons. -’s experiment: α-particles mostly pass; some deflected, revealing nucleus.
• Nucleus: dense, positively charged core containing protons and neutrons.
• Proton number (Z): defines the element; unique for each element.
• Isotopes: same Z, different A (mass number); e.g., hydrogen isotopes.
• Radioactive decay: spontaneous emission of α, β, or γ radiation.
• Half-life (T₁/₂): time for half the radioactive sample to decay.
• Types of radiation:
  • α: helium nucleus, high ionization, short range.
  • β: electrons, moderate ionization, longer range.
  • γ: electromagnetic waves, low ionization, high penetration.
• Nuclear fission: splitting of heavy nucleus into lighter nuclei + energy.
• Nuclear fusion: combining light nuclei to form heavier nuclei + energy.
• Hazards: burns, mutations, leukemia; require safety precautions.

2. 🧩 Key Structures & Components

• Nucleus — central core, contains protons and neutrons, positive charge.
• Protons — positively charged particles, Z determines element.
• Neutrons — neutral particles, contribute to atomic mass.
• Electrons — negatively charged particles in orbitals.
• Nuclide notation — XZ A (X= element, Z= atomic number, A= nucleon number).
• Radioactive isotopes — unstable variants used in medicine, industry.
• α-particles — helium nuclei, +2 charge, high ionization.
• β-particles — electrons, −1 charge, moderate ionization.
• γ-rays — electromagnetic radiation, neutral, penetrating.

3. 🔬 Functions, Mechanisms & Relationships

• Nucleus: dense center, holds protons/neutrons, responsible for atomic mass.
• Radioactive decay:
  • α-decay decreases Z by 2, A by 4.
  • β-decay increases Z by 1, A unchanged.
  • γ-emission releases energy without changing Z or A.
• Radiation detection:
  • α: deflected toward negative plate.
  • β: deflected toward positive plate.
  • γ: unaffected by electric/magnetic fields.
• Decay chain: successive emissions lead to stable isotope.
• Fission:
  • Heavy nucleus absorbs neutron → unstable → splits.
  • Chain reaction: neutrons trigger further fission.
• Fusion:
  • Light nuclei combine, releasing energy.
  • Example: D + T → He + neutron + energy.
• Half-life:
  • Decay follows exponential law: N = N₀ (1/2)^(T / T₁/₂).
  • Used in radiocarbon dating.

4. 📊 Comparative Table

Item	Key Features	Notes / Differences
α-particles	Helium nucleus, +2 charge, high ionization, short range	Stopped by paper, dangerous if ingested
β-particles	Electrons, −1 charge, moderate ionization, longer range	Stopped by aluminum foil, penetrates tissue
γ-rays	Electromagnetic waves, neutral, high penetration	Requires lead shielding, passes through tissue

5. 🗂️ Hierarchical Diagram

Radioactivity
 ├─ Types of Radiation
 │    ├─ α: helium nucleus, +2 charge
 │    ├─ β: electrons, −1 charge
 │    └─ γ: electromagnetic waves
 ├─ Decay Processes
 │    ├─ α-decay: Z−2, A−4
 │    ├─ β-decay: Z+1, A unchanged
 │    └─ γ-emission: energy release
 └─ Applications & Hazards

6. ⚠️ High-Yield Pitfalls & Confusions

• Confusing α and β radiation: α is helium nucleus, β is electron.
• Assuming γ radiation is harmless: high penetration, requires heavy shielding.
• Miscalculating decay: forgetting to update Z and A after decay.
• Mixing isotopes: Z determines element, A determines isotope.
• Overlooking safety: not using shielding or proper disposal.
• Believing all radioactive decay is slow: some isotopes decay rapidly.
• Confusing nuclear fission with fusion: splitting vs. combining nuclei.
• Ignoring background radiation in measurements.

7. ✅ Final Exam Checklist

• Define atom, nucleus, proton, neutron, electron.
• Explain Rutherford’s experiment and its significance.
• Describe the structure of the nucleus.
• State the meaning of proton number (Z) and nucleon number (A).
• Write nuclide notation: XZ A.
• List types of radiation: α, β, γ, with properties.
• Describe how α, β, γ are detected.
• Explain radioactive decay and half-life.
• Write decay formula: N = N₀ (1/2)^(T / T₁/₂).
• Differentiate fission and fusion.
• Describe chain reactions in nuclear reactors.
• List applications of radioisotopes in medicine and industry.
• Identify safety measures for handling radioactivity.
• Recognize common hazards: burns, mutations, leukemia.
• Understand the importance of shielding and proper disposal.
• Be familiar with decay chains and stability of isotopes.

This revision sheet condenses core concepts, structures, and relationships for exam success in Unit 18: Radioactivity.