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Nuclear Chemistry

Nuclear Chemistry. Images. http://www.pbs.org/wgbh/nova/physics/stability-elements.html http://player.discoveryeducation.com/index.cfm?guidAssetID=D2253610-8B06-462A-889D-04A63D6A9A77&productcode=US. Nuclear Decay. Why nuclides decay… need stable ratio of neutrons to protons.

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Nuclear Chemistry

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  1. Nuclear Chemistry

  2. Images • http://www.pbs.org/wgbh/nova/physics/stability-elements.html • http://player.discoveryeducation.com/index.cfm?guidAssetID=D2253610-8B06-462A-889D-04A63D6A9A77&productcode=US

  3. Nuclear Decay • Why nuclides decay… • need stable ratio of neutrons to protons DECAY SERIES TRANSPARENCY

  4. Radiation • Radiation-it’s the transfer of energy • Radioactivity-The spontaneous emission of radiation by an unstable nucleus.

  5. Good vs. Bad • Ionizing • Has enough energy to kick off an ion. • Very high energy • Non ionizing • Does not have enough energy to kick off an ion • Low energy

  6. Types of Radiation • Alpha particle () • helium nucleus paper 2+ • Beta particle (-) • electron lead 1- • Gamma () • high-energy photon concrete 0

  7. parent nuclide alpha particle daughter nuclide Nuclear Decay • Alpha Emission Numbers must balance!!

  8. electron Nuclear Decay • Beta Emission

  9. electron Nuclear Decay • Electron Capture • Gamma Emission • Usually follows other types of decay. • Transmutation • One element becomes another.

  10. Half-life • Half-life (t½) • Time required for half the atoms of a radioactive nuclide to decay. • Shorter half-life = less stable.

  11. Half-life mf:final mass mi:initial mass n:# of half-lives

  12. Half-life n: # of half lives t1/2 : half life

  13. Half-life mf:final mass mi:initial mass n:# of half-lives

  14. Half-life • Fluorine-21 has a half-life of 5.0 seconds. If you start with 25 g of fluorine-21, how many grams would remain after 60.0 s? GIVEN: t½ = 5.0 s mi = 25 g mf = ? total time = 60.0 s n = 60.0s ÷ 5.0s =12 WORK: mf = mi (½)n mf = (25 g)(0.5)12 mf = 0.0061 g

  15. Half-life • A sample of a radioactive isotope that was initially 5000 g decayed for 10,000 years. If 625 g remains after this time, what is the half-life of the isotope? GIVEN: t½ = ? mi = 5000 g mf = 625 g total time=10000yrs n = ? WORK: n= n =3 n= total time ÷t1/2 t1/2 = total time/n t1/2= 10000 ÷ 3 t1/2 = 3333.33 yrs.

  16. Half-life • Or plug into the equation and solve: GIVEN: t½ = ? mi = 5000 g mf = 625 g total time=10000yrs n = ? WORK: mf=mi(1/2)n 625g = (5000) (1/2)n .125=(1/2)n ln(.125)÷ln(1/2) =n n=3 then plug into n=total time ÷ t1/2

  17. Fission • splitting a nucleus into two or more smaller nuclei • 1 g of 235U = 3 tons of coal

  18. Fission • chain reaction - self-propagating reaction • critical mass - the minimum amount of fissionable material needed to sustain a chain reaction

  19. Fission • Uranium-235 is the only naturally occurring element that undergoes fission. Uranium - 235

  20. Fission • Why does fission produce so much energy? • Small quantities of mass are converted into appreciable quantities of energy. E = mc2

  21. Fission Energy 1 gram matter 700,000 Gallons of high octane gasoline

  22. http://player.discoveryeducation.com/index.cfm?guidAssetID=35b0a19c-b72d-4502-92af-6cb6c9078cc9&productcode=UShttp://player.discoveryeducation.com/index.cfm?guidAssetID=35b0a19c-b72d-4502-92af-6cb6c9078cc9&productcode=US

  23. Fusion • combining of two nuclei to form one nucleus of larger mass • thermonuclear reaction – requires temp of 40,000,000 K to sustain • 1 g of fusion fuel = 20 tons of coal • occurs naturally in stars

  24. 235U is limited danger of meltdown toxic waste thermal pollution fuel is abundant no danger of meltdown no toxic waste not yet sustainable Fission vs. Fusion FISSION FUSION

  25. Cooling Tower Nuclear Power • Fission Reactors

  26. Nuclear Power • Fission Reactors

  27. Nuclear Power • Fusion Reactors (not yet sustainable)

  28. Nuclear Power • Fusion Reactors (not yet sustainable) National Spherical Torus Experiment Tokamak Fusion Test Reactor Princeton University

  29. Synthetic Elements • Transuranium Elements • elements with atomic #s above 92 • synthetically produced in nuclear reactors and accelerators • most decay very rapidly

  30. Radioactive Dating • half-life measurements of radioactive elements are used to determine the age of an object • decay rate indicates amount of radioactive material • EX: 14C - up to 40,000 years238U and 40K - over 300,000 years

  31. Radiation treatment using -rays from cobalt-60. Nuclear Medicine • Radioisotope Tracers • absorbed by specific organs and used to diagnose diseases • Radiation Treatment • larger doses are used to kill cancerous cells in targeted organs • internal or external radiation source

  32. Nuclear Weapons • Atomic Bomb • chemical explosion is used to form a critical mass of 235U or 239Pu • fission develops into an uncontrolled chain reaction • Hydrogen Bomb • chemical explosion  fission  fusion • fusion increases the fission rate • more powerful than the atomic bomb

  33. Others • Food Irradiation •  radiation is used to kill bacteria • Radioactive Tracers • explore chemical pathways • trace water flow • study plant growth, photosynthesis • Consumer Products • ionizing smoke detectors - 241Am

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