Radiation Hazards

Radiation Basics & Units - Watts Up, Doc?

• Types:
  • Ionizing: X-rays, Gamma, $\alpha$, $\beta$, Neutrons. Ejects electrons.
  • Non-ionizing: UV, visible, IR, microwave, RF.
• Core Concepts:
  • Radioactivity: Spontaneous nuclear emission.
  • Half-life ($T_{1/2}$): Time for 50% decay.
• Key Units:
  • Activity: Becquerel (Bq) [SI], Curie (Ci). $1 \text{ Ci} = 3.7 \times \textbf{10}^{10} \text{ Bq}$.
  • Absorbed Dose (D): Gray (Gy) [SI], rad. $1 \text{ Gy} = \textbf{100} \text{ rad}$. (Energy/mass).
  • Equivalent Dose (H): Sievert (Sv) [SI], rem. $1 \text{ Sv} = \textbf{100} \text{ rem}$. $H = D \times Q$ (Q=Quality Factor).
  • Effective Dose (E): Sievert (Sv). $E = \sum (H_T \times W_T)$ (tissue weighting).
  • 📌 Mnemonic: Gray = absorbed anywhere; Sievert = biological severity.

⭐ Sievert (Sv) quantifies biological damage for both Equivalent and Effective Dose.

Biological Effects - Cellular Mayhem

• Radiation induces cellular damage through two primary mechanisms:

  • Direct Action: Radiation directly ionizes critical macromolecules (DNA, proteins). Predominant with high-LET radiation (e.g., α particles, neutrons).
  • Indirect Action: Radiation interacts with cellular water (radiolysis), producing highly reactive free radicals (e.g., OH•, H•, $e_{aq}^{-}$). These radicals then damage biomolecules. Accounts for ~70-80% of damage from low-LET radiation (X-rays, γ-rays).

• Primary Cellular Target: DNA

  • Damage types: Base alterations, single-strand breaks (SSBs), double-strand breaks (DSBs).
  • DSBs are the most lethal lesions, often leading to cell death, mutations, or chromosomal aberrations if misrepaired.

• Cellular Responses to Damage:

  • Repair: Enzymatic correction (e.g., BER, NHEJ).
  • Cell Cycle Arrest: Checkpoints (G1/S, S, G2/M) allow time for repair.
  • Apoptosis: Programmed cell death for severely damaged cells.
  • Mitotic Catastrophe: Cell death during or after faulty mitosis.
  • Senescence: Irreversible growth arrest.
  • Neoplastic Transformation: Potential for carcinogenesis.

• Law of Bergonié & Tribondeau: Cells are more radiosensitive if they: 📌 MUM's cells are sensitive

  • Have high Mitotic activity.
  • Are Undifferentiated.
  • Undergo Many future mitoses.

  ⭐ Cells in G2/M phase are generally the most radiosensitive, while late S phase cells are the most radioresistant.

Radiation Protection & Limits - Shields Up!

• ALARA Principle: As Low As Reasonably Achievable.
  • Minimize Time.
  • Maximize Distance (Inverse square law: $I \propto 1/d^2$).
  • Use Shielding (📌 Mnemonic: TDS).
• Shielding Materials:
  • Lead (Pb): X-rays, Gamma rays.
  • Concrete: Gamma rays.
  • Perspex: Beta particles.
• Occupational Dose Limits (AERB/ICRP):
  • Effective Dose: 20 mSv/year (averaged over 5 years); max 50 mSv in one year.
  • Lens: 20 mSv/year.
  • Skin/Extremities: 500 mSv/year.
• Public Dose Limit: Effective Dose 1 mSv/year.
• Pregnancy (Occupational): Foetus < 1 mSv after declaration.

⭐ Annual occupational dose limit for the lens of the eye is 20 mSv/year.

Forensic Radiation - Glowing Evidence

• Medico-legal: Investigates radiation death/injury under BNS provisions for causing hurt by dangerous means.
• Types: α, β, γ, X-rays, Neutrons.
• Units: Gray (Gy) - absorbed dose; Sievert (Sv) - biological effect.
• Modern Analysis: CT, MRI, 3D reconstruction, digital evidence protocols per BNSS procedures.
• Effects:
  • Deterministic (threshold): Acute Radiation Syndrome (ARS), skin burns, sterility. Severity dose-dependent.
  • Stochastic (no threshold): Cancer (leukemia, thyroid), genetic. Probability dose-dependent.
• ARS Syndromes:
  • Hematopoietic (2-10 Gy)
  • Gastrointestinal (10-50 Gy)
  • Neurovascular (>50 Gy)
• Forensic Analysis: Scene dosimetry, autopsy (bone marrow, GIT), molecular biodosimetry, cytogenetic methods.
• Biosafety: Current infection control for contaminated samples per international guidelines.

⭐ Whole body lethal dose (LD50/60) is approximately 4-5 Gy without medical intervention

High‑Yield Points - ⚡ Biggest Takeaways

• Deterministic effects (e.g., skin burns) have a threshold dose; stochastic effects (e.g., cancer) do not.
• Most radiosensitive: Bone marrow, gonads, lymphoid tissue, intestinal epithelium. Least: Muscle, nerve.
• Acute Radiation Syndrome (ARS): Prodromal, Latent, Manifest illness phases; key syndromes are Hematopoietic (2-10 Gy), Gastrointestinal (10-50 Gy), Neurovascular (>50 Gy).
• LD50/60 (whole-body): 3.5-4.5 Gy without medical support.
• Late effects: Leukemia, thyroid cancer, cataracts, genetic mutations.
• Protection principles: Time (minimize), Distance (maximize), Shielding.