Biological effects of ionizing radiation. Hygienic problems related to the use of radioactive substances and sources of ionizing radiation in various industries.
1. Biological Effects of Ionizing Radiation
A) Ionizing radiation damages cells and tissues mainly through direct and indirect actions.
- Direct action: Ionizes DNA, proteins, lipids → structural damage, mutations.
- Indirect action (main): Radiation interacts with water molecules and cells causing radiolysis of water → reactive radicals (OH•, H₂O₂, HO₂•) → oxidative cellular damage.
B) Cells exposed to radiation may experience:
- No damage
- Damage repaired
- develop persistent mutations (which can lead to cancer)
- Cell death
C) Tissue Sensitivity: Rapidly dividing or young tissues are most sensitive: bone marrow, gastrointestinal lining, gonads, thyroid, fetus (especially early organogenesis).
D) Types of Effects
- Deterministic (Non-Stochastic) Effects:
- Threshold dose required; severity increases with dose.
- Examples: Skin burns (500–1200 cSv), hair loss, cataracts (~200 cSv), Acute Radiation Syndrome (hematopoietic, gastrointestinal, CNS, cutaneous), fetal/embryo damage (~10 cSv).
- Stochastic (Non-Threshold) Effects:
- Probability increases with dose, severity independent of dose.
- Examples: Cancer (leukemia, thyroid, bone, lung), hereditary mutations; latency: 10–25 years.
E) Factors Influencing Effects
- Dose magnitude and rate (acute high dose > prolonged low dose)
- Radiation type: α > β > γ (per unit energy)
- Organ sensitivity
- Age and health status (children and elderly more vulnerable)
3. Sources of Ionizing Radiation
A) Natural Sources
- Cosmic rays: From outer space and the sun.
- Radioactive elements in soil and water: Uranium, Radium, Thorium.
- Atmospheric Radon gas (from uranium decay):
- Invisible and odorless, accumulates in enclosed spaces.
- Leading cause of lung cancer in non-smokers.
- Prevention: Daily ventilation, continuous airflow, sealing cracks.
- Naturally occurring isotopes: Potassium-40 (K-40), Strontium-90 (Sr-90).
B) Man-Made Sources
- Medical: X-ray equipment, radiotherapy, nuclear medicine.
- Industrial: Radiography, non-destructive testing (NDT).
- Energy production: Nuclear power plants (Uranium, Plutonium, reactor emissions).
- Research: Radioisotope production laboratories.
4. Radiation Types, Penetration, Hazards, and Shielding
1. Alpha (α) Radiation
- Source: helium nucleus from heavy elements (U, Ra, Rn).
- Penetration: very low, cannot pass intact skin.
- Hazard: dangerous if inhaled/ingested (internal organs), can irradiate sensitive tissues (lungs, digestive tract and bone marrow).
- Shielding: paper or gloves.
2. Beta (β) Radiation
- Source: high-speed electrons from radioactive atoms.
- Penetration: shallow, can slightly penetrate skin.
- Hazard: skin burns, eye/tissue damage with prolonged exposure.
- Shielding: plastic, glass, aluminum.
3. Gamma (γ) Radiation
- Source: high-energy photons from the nucleus.
- Penetration: highly penetrating, whole-body hazard.
- Shielding: dense materials (lead, concrete).
4. X-rays
- Source: photons from electron interactions (not nucleus).
- Penetration: similar to low-energy gamma rays.
- Hazard: cumulative damage in medical/industrial settings.
- Shielding: lead barriers, aprons, wall