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Lecture 5

Lecture 5 Summary.docx

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BIOL 354
Bruce Greenberg

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BIOL354 – Environmental Toxicology I Spring 2012 Lecture 5: Radioactivity - Review: PAHs can be anthropogenic or can be naturally emitted through volcanic activity & forest fires. - Radioactive Elements & Isotopes: o Naturally occurring radioisotopes @ low level o Anthropogenic Sources: (CONCERN)  Mining of the reactor fuel - Uranium  Normal operational release of nuclear plants  Accidental releases from nuclear reactors & power plants  Medical or industrial effluents containing radioactive isotopes  Reprocessing of DU for Uranium weapons  Storage of DU @ nuclear cores o Uranium (6 isotopes, all radioactive/unstable)  Naturally occurring Uranium consists of U-238 (99.2%) & U-235 (0.72%).  U-235 can undergo spontaneous fission; the predominant U-238 is not fissile.  Neutron of 1 U-235 strikes the nucleus of the 2 U-235, 2 nucleus splits into fission fragments + 2 more neutrons + photons (energy) -> cycle.  U-235 Self-Sustaining Nuclear Fission Chain Reaction -> highly exothermic.  Uranium Enrichment: Removal of some U-238 [U-235 + U-238 = 100%]  Critical Mass: smallest amount of fissile material (U-235) needed to sustain NCR.  Slow & Long-lasting NCR (Nuclear Reactor Grade): Low enriched U-235 (3-4%)  Rapid & Short-duration NCR (Nuclear Weapon Grade): High enriched U-235 (90%)  Depleted Uranium (DU): U-238, by-products of Uranium Enrichment  Extremely dense, less radioactive than natural Uranium (removal of U-235).  Radiation Shield (Medical Clinic) & Armor Piercing Projectile (War).  DU has no biological role = Toxic Metal o Adversely effects major organs & continual exposure -> birth defects. o Radioactive t½ = 4.468 bil years, biological t½ = 15 days. o Powder produced during impact/combustion of DU munitions (Uranium Bullets) can spread & contaminate areas around.  Iraq: 2000 tonnes DU munitions -> inhalation -> elevated number of cancers & birth defect s. - Radioisotopes: Unstable isotopes undergoing spontaneous “decay” to lose excessive neutrons. o Isotopes: Same proton # but different neutron # (Check atomic mass #)  Different proton # = Different element; Different neutron # = Stable or Unstable element. o Ionizing Radiation: Sub-Atomic Particles (α & β) & Electro-Magnetic Radiation (γ-rays & X-rays)  Exponential Decay, rate is the isotopes’ half-life (t½ <<1s to > 1000yrs).  Rapid decline @ beginning & later slows down (Never 0 regardless of the # of t½s). - The Electromagnetic Spectrum o Non-ionizing Radiation (Grey area): Lower energy photons.  Longer wavelength = Lower frequency = Lower energy = Less dangerous  Radio waves & light (infrared, visible & aV )  Radiation generated by Human > Radiation generated y Microwave o Ionizing Radiation: Enough energy per photon to ionize atoms or molecules (Higher energy photons)  Shorter wavelength = Higher frequency = Higher energy = Dangerous  Tissue penetration & DNA bond breakage (UV ,bX-ray, γ-rays)  The e & p leads to ROS (free radical) generation in biological systems. BIOL354 – Environmental Toxicology I Spring 2012 - Ionizing Radiation: First releases α or β particles & then γ-rays or x-rays o After fission (release of Alpha or Beta particles)  UNSTABLE, EXCITED daughter nucleus - γ-rays = Lower energy Ground State o Alpha (α) Particles = He (Ejected chunk of nucleus with a+charge) +  Large subatomic particle (2x protons & 2x neutrons)  New Atomic Mass # (Proton + Neutron) = Original – 4, new element.  New Atomic # (Proton) = Original -2 o Parent Uranium-235 – Helium Nucleus (α) = Daughter Thorium-231  Highly ionizing, minimal penetrating depth due to its huge size  Protection: Stopped by few cm of air, skin, sheet of paper, etc.  Ingestion: Extremely dangerous o Beta (β) Particles (2 types depending on whether electrons or positrons are generated) -  Electron (β decay) (99.9%) Excess neutrons, 1 neutron converted to 1 proton & 1 electron  Positron (β decay) (0.1%) Excess protons, 1 proton converted to 1 positron  Positron (anti-electrons): + charged electron  High speed, very small, travels further  Less ionizing, can penetrate peripheral tissue & damage external organs due to small size.  Protection: Stopped by a layer
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