Radiation Exposure and Safety

Radiation Basics - Zap Fundamentals

• Types of Ionizing Radiation:
  • Particulate: Alpha (α), Beta (β), Neutrons (n).
    • α: Large, +2 charge, high Linear Energy Transfer (LET), low penetration (paper).
    • β: Small, ±1 charge, moderate LET & penetration (thin aluminum).
  • Electromagnetic (Photons): Gamma (γ), X-rays.
    • γ/X-rays: No charge/mass, low LET, high penetration (lead, concrete).
• Key Units:
  • Absorbed Dose: Gray (Gy) - energy deposited per unit mass (J/kg).
  • Equivalent Dose: Sievert (Sv) - Gy x Radiation Weighting Factor ($W_R$). Accounts for biological effectiveness.
  • Activity: Becquerel (Bq) - 1 disintegration/sec. Curie (Ci) - 3.7 x $10^{10}$ Bq.
• Sources:
  • Natural: Cosmic rays, terrestrial (radon, thoron), internal (K-40).
  • Man-made: Medical (X-rays, CT), industrial, nuclear fallout.

⭐ Alpha particles, despite low penetration, are highly damaging if internalized (ingested/inhaled) due to their high LET causing dense ionization tracks. This makes internal emitters like Radon-222 particularly hazardous for lung tissue.

Biological Effects - Cellular Shockwaves

• Rapid Cascade (Cellular Shockwave): Initial energy deposition & ionization ($<10^{-15}$ s) → free radical formation (indirect action, $10^{-12}$ to $10^{-6}$ s) → biomolecular damage (microseconds to seconds).
• Mechanisms of Damage:
  • Direct Action: Radiation directly ionizes critical macromolecules (DNA, proteins). Predominant with high-LET radiation (α-particles, neutrons).
  • Indirect Action: Radiation interacts with cellular $H_2O$ (radiolysis), creating reactive free radicals (e.g., $\cdot OH$, $H\cdot$). These diffuse to damage targets.

    ⭐ Indirect action via water radiolysis accounts for ~70% of DNA damage from X-rays & γ-rays (low-LET).

• Primary Target: DNA
  • Damage types: Single-Strand Breaks (SSBs), Double-Strand Breaks (DSBs), base alterations, crosslinks.
  • DSBs are most critical for cell lethality, mutations, and carcinogenesis.
• Cellular Fate: Depends on damage extent: successful repair, apoptosis (programmed cell death), senescence, or genomic instability leading to cancer.

Radiation Protection - Shield Up!

• ALARA Principle: "As Low As Reasonably Achievable" guides all radiation safety practices.
• Three Cardinal Rules (📌 TDS):
  • Time: ↓ exposure time = ↓ dose.
  • Distance: ↑ distance from source = ↓ dose. Intensity decreases with square of distance ($I \propto 1/d^2$).
  • Shielding: Use appropriate barriers.
    • Lead (Pb) for X-rays & gamma rays.
    • Concrete for high-energy gamma & neutrons.
    • Perspex/Lucite for beta particles.
• Personnel Monitoring: Dosimeters (e.g., TLD, film badge) track individual exposure.
• Controlled & Supervised Areas: Demarcated zones with restricted access & specific safety protocols.

⭐ The inverse square law is a cornerstone of radiation protection: doubling the distance from a point source reduces the radiation intensity to one-quarter ($1/4$).

Exposure Management - Damage Control

• Initial Steps & Decontamination:
  • Remove victim from source immediately.
  • Remove clothing (↓ dose up to 90%).
  • External decontamination: wash (soap/water); cover wounds.
• Internal Contamination (Decorporation):
  • Blocking: KI (130 mg) for $^{131}I$.
  • Chelation:
    • Prussian Blue: Caesium ($^{137}Cs$), Thallium.
    • DTPA (Ca/Zn): Plutonium, Americium.
  • Dilution: Water for Tritium ($^3H$).
• Medical Management (ARS):
  • Supportive: antiemetics, fluids, pain relief, antibiotics.
  • Hematopoietic (>1 Gy): G-CSF/GM-CSF; HSCT if >6-8 Gy.
  • GI (>6 Gy): IV fluids, electrolytes, gut rest.
  • Neurovascular (>20 Gy): Palliative care.
• Rescuer Safety: TDS; PPE.

⭐ Early onset of vomiting (<1 hour) post-exposure suggests a severe dose (>4 Gy), guiding triage.

High‑Yield Points - ⚡ Biggest Takeaways

• Deterministic effects: threshold dose, severity ↑ with dose (e.g., skin erythema, cataracts).
• Stochastic effects: no threshold, probability ↑ with dose (e.g., cancer, genetic effects).
• ALARA (As Low As Reasonably Achievable) is the guiding principle for radiation safety.
• Minimize exposure via Time (↓), Distance (↑), and Shielding.
• Most radiosensitive: lymphoid, bone marrow, gonads, intestinal epithelium.
• Acute Radiation Syndrome (ARS): prodromal, latent, manifest illness, recovery/death stages.
• Potassium Iodide (KI) protects thyroid from radioactive iodine exposure during nuclear incidents.