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radiation CHM 102/Sinex radiation

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  • 1. radiation CHM 102/Sinex
  • 2. radiation ionize electrons break bonds Source: http://www.arpansa.gov.au/basics/ion_nonion.htm
  • 3. Which form of radiation is the most penetrating? Which form of radiation is the most biological damaging? …and now ionizing radiation
  • 4. α β γ paper 0.5 cm lead 10 cm lead Penetrating Power of Radiation Relative penetration power α:β:γ 1:100:10,000
  • 5. Most penetrating form of radiation? Easiest form of radiation to shield from? α β γ α β γ wrong wrong wrong wrongcorrect correct …and now a pop quiz
  • 6. OH . (hydroxyl radical) H . Radiation Damage water molecule γ-ray 2 OH .  H2O2 What happens when the water molecule is struck by the gamma ray?
  • 7.  All forms of nuclear radiation are considered ionizing radiation. There energy is large enough to ionize electrons from a molecule. H2O  H2O+ + e-  Ar  Ar+ + e- This formation of ion pairs is the basis of the Geiger Counter.  In some cases even bonds are broken. The products formed can be extremely reactive, such as the OH . radical!  See how water and radiation can interact or the radiolysis of water – click here
  • 8. Radiation Damage Radiation weighting factor, WR or relative damage that can be caused in a biological system. Radiation WR alpha 20 fast neutron 10 slow neutron 5 beta 1 gamma rays 1 Increasingbiologicaldamage Source: http://www.euronuclear.org/info/encyclopedia/d/dose.htm
  • 9. Why does an alpha particle have a high WR or cause a large amount of biological damage? Although alpha particles travel only short distances, they are massive and cause major damage in their path. answer Alpha particles are much more dangerous when inhaled or ingested compared to external exposure. Why? answer Clothes and dead skin cells provide shielding externally, while internally alpha particles have direct contact with cells.
  • 10. Radiation detection Ar (g) incoming radiation α, β , or γ Ion pair formation: Ar  Ar+ + e- Geiger-Mueller tube High voltage 800-1200 v thin window of mica anode + cathode - Current flows due to production of ion pairs.
  • 11. Radiation Protection 0 100 200 300 400 500 600 0 1 2 3 4 5 6 Distance (m) Activity(cpm) U source detector start How does the radiation level vary if the detector is moved away?
  • 12. Radiation Protection 0 100 200 300 400 500 600 0 1 2 3 4 5 6 Distance (m) Activity(cpm) U source detector
  • 13. Radiation Protection 0 100 200 300 400 500 600 0 1 2 3 4 5 6 Distance (m) Activity(cpm) U source detector
  • 14. Radiation Protection 0 100 200 300 400 500 600 0 1 2 3 4 5 6 Distance (m) Activity(cpm) U source detector
  • 15. Radiation Protection 0 100 200 300 400 500 600 0 1 2 3 4 5 6 Distance (m) Activity(cpm) U source detector
  • 16. Distance, m Activity, cpm 1.0 500.0 2.0 125.0 3.0 55.6 4.0 31.3 5.0 20.0 Derive the mathematical relationship between activity and distance. 2 d 500 A = This is known as the inverse square law. The intensity of the radiation drops as the square of the distance. answer
  • 17. Radiation protections involves: • Shielding • Distance • Time of exposure So use these three factors to address the next slide.
  • 18. 1 2 3 4 highly radioactive γ-source Rank the laboratory workers in terms of their safety safest: _____ > _____ > _____ > _____ lead-lined walls 2 4 3 1 How could person 1 improve there hazardous situation? Limit time of exposure!
  • 19. Large-scale Nuclear Reactions Natural uranium: 0.7% 235 U, 99.3% 238 U Nuclear reactors: 3 - 4% 235 U enriched 235 U as fuel in US commercial electric power production – controlled fission Nuclear weapons: 90% 235 U enriched atomic bomb: uncontrolled fission 235 U 239 Pu (Pu produced in spent fuel of nuclear reactors) H-bomb: fission-fusion - larger scale energy release How do you separate isotopes, same chemistry? different kinetics!
  • 20. Isotope separation Calutron: production-scale mass spectrometer to separated uranium metal ions (235 U for Hiroshima bomb) gaseous diffusion: Graham’s Law used UF6 (s)  UF6 (g) at 56o C to separate 235 UF6 from 238 UF6 gas centrifuge: spin mixture of 235 UF6 and 238 UF6 heavier gas to outside, lighter in center http://en.wikipedia.org/wiki/Enriched_uranium
  • 21. World map of nuclear reactors http://www.insc.anl.gov/pwrmaps/map/world_map.php Where are most nuclear reactors located?
  • 22. http://www.ocrwm.doe.gov/factsheets/doeymp0010.shtml Oklo: Natural Nuclear Reactors 1.7 – 1.8 billion year old rock Level of 235 U was ~3% at that time TODAY-  Many isotopes common in spent nuclear reactor fuel occur in rock  235 U is depleted to as low as 0.44% (most 0.7%)  239 Pu was naturally produced at Oklo
  • 23. Nuclear weapons Explosive power: 1 megaton = 106 tons of TNT Largest H-bomb tested: Tsar Bomba (Russia) 50 Mtons Atomic bombs used in wartime – Hiroshima: 60 kg 235 U 13 kilotons 90,000 deaths – Nagasaki: ~6.4 kg 239 Pu 21 kilotons 70,000 deaths http://en.wikipedia.org/wiki/Atomic_bombings_of_Hiroshima_and_Nagasaki
  • 24. Fallout (airborne radionuclides) from weapons testing and reactor accidents • Atmospheric testing of nuclear weapons – 90 Sr in milk • Nuclear reactor accidents – Three Mile Island: 1979, radioactive gases released (Kr) – Chernobyl: 1986, radioactive nuclear fuel dispersed by chemical explosion, radiation measured globally!
  • 25. What is the largest source of to the average person? What is the largest source of background radiation to a person that smokes? Natural background radiation
  • 26. Sources of Background Radiation Estimate your background radiation exposure – click here Source: http://web.princeton.edu/sites/ehs/osradtraining/backgroundradiation/background.htm If you smoke
  • 27. Radioactive sources in your house Smoke detector 241 Am Gas mantles for camping lanterns 232 Th Constant glowing watch dials 3 H or 147 Pm while older vintage watches (pre-1970’s) 226 Ra Vintage orange plates Fiesta Ware and some older Cloisonné Jewelry 238 U based ceramic glaze http://hps.org/documents/consumerproducts.pdf
  • 28. Applications of Isotopes Nuclear medicine for diagnosis and treatment Food irradiation to control pathogenic and spoilage bacteria 99m Tc, t1/2 = 6 hours, workhorse in nuclear medicine 131 I, t1/2 = 8 days, is used to diagnose and treat thyroid disorders 60 Co and 137 Cs radioisotopes Modern irradiation is mostly done with x-rays.
  • 29. Dating objects Can determine N/No ratio using mass spectroscopy and calculate tage Consider using tritium, 3 H, with a half-life of 12.32 yrs Present day rain water – 32 pCi/L water = No A 12 year old bottle of wine – 16 pCi/L A 25 year old bottle of scotch - 8 pCi/L 14 C with a t1/2 = 5730 yr is used in archeology Parent/Daughter used in Earth Sciences for rocks an meteorites 235 U/207 Pb 0.704 by 40 K/40 Ar 1.25 by 238 U/206 Pb 4.47 by 87 Sr/87 Rb 48.8 by
  • 30. CH3 C OH O CH3 CH2 OH CH3 C O CH2 CH3 O H OH CH3 C O CH2 CH3 O H OH + + + Which OH group is removed? 16 O 18 O Reaction mechanisms in chemistry The oxygen in the acetic acid is 16 O, while the ethanol contains 18 O. Which molecules does the OH group get removed from? The two paths below illustrate the possible reactions. The 18 O is all found in the ester. answer stable isotopes Mass spectroscopy is used to determine distribution of isotopes.