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Section 4.4 Unstable Nuclei and Radioactive Decay

Section 4.4 Unstable Nuclei and Radioactive Decay. Explain the relationship between unstable nuclei and radioactive decay. Characterize alpha, beta, and gamma radiation in terms of mass and charge.

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Section 4.4 Unstable Nuclei and Radioactive Decay

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  1. Section 4.4 Unstable Nuclei and Radioactive Decay • Explain the relationship between unstable nuclei and radioactive decay. • Characterize alpha, beta, and gamma radiation in terms of mass and charge. element: a pure substance that cannot be broken down into simpler substances by physical or chemical means

  2. Section 4.4 Unstable Nuclei and Radioactive Decay (cont.) radioactivity radiation nuclear reaction radioactive decay alpha radiation alpha particle nuclear equation beta radiation beta particle gamma rays Unstable atoms emit radiation to gain stability.

  3. Radioactivity • Nuclear reactions can change one element into another element. • In the late 1890s, scientists noticed some substances spontaneously emitted radiation, a process they called radioactivity. • The rays and particles emitted are called radiation. • A reaction that involves a change in an atom's nucleus is called a nuclear reaction. • Atoms are radioactive because they have too much energy !!!!

  4. Radioactive Decay • Unstable nuclei lose energy by emitting radiation in a spontaneous process called radioactive decay. • Unstable radioactive elements undergo radioactive decay thus forming stable non-radioactive elements.

  5. Balancing Nuclear equations • The figure shown below is a nuclear equation showing the radioactive decay of Plutonium 239 producing an alpha particle 23994Pu → 42He + _____ • The mass is conserved in nuclear equations, meaning the atomic number and mass number must be equal on both sides of the equation.

  6. Types of Radiation • Alpha radiation is made up of positively charged particles called alpha particles. • Each alpha particle contains two protons and two neutrons and has a 2+ charge.

  7. Types of Radiation • Beta radiation is radiation that has a negative charge and emits beta particles. • Each beta particleis an electron with a 1– charge.

  8. Types of Radiation • Gamma raysare high-energy radiation with no mass and are neutral. • Gamma rays account for most of the energy lost during radioactive decay.

  9. Gamma Radiation has no mass, so the same isotope is left after radioactive decay

  10. Radioactive Decay (cont.)

  11. Radioactive Decay (cont.) • Atoms that contain too many or two few neutrons are unstable and lose energy through radioactive decay to form a stable nucleus. • Few exist in nature—most have already decayed to stable forms.

  12. Nuclear Fission:Nuclear Energy - Nuclear Power PlantsHalf Life – Nuclear Waste

  13. Nuclear Fission: splitting of the atom (or nucleus) • Otto Hahn & Fritz Strassman (Meitner & Frisch) Energy is released when the nucleus splits (Dark force) This energy is why we have nuclear power plants (and bombs)

  14. Fission Chain Reaction

  15. Fuel Rods • Large tubes that are filled with the rods of radioactive material • Usually uranium oxide or uranium hexafluoride

  16. How do we control the reaction?Control Rods: Catch extra neutrons

  17. How a Nuclear Plant Generates Energy Fig.07.07

  18. Nuclear Power Plant • Work just like fossil fuel power plants • Heat turns water to steam, steam turns turbine, creating electricity • Two portions • Nuclear reactor • Non-nuclear part • Fuel = UO2 pellets • Control Rods = cadmium, function is to absorb neutrons

  19. “The China Syndrome”? • Meltdown (out of control chain reaction) of uranium core • Heat is so intense, melts rock all the way to China! • Could it happen ??????

  20. Chornobyl, Part of USSR, now Ukraine (April 26, 1986)

  21. Chornobyl • During Safety Test, cut off flow of cooling water • Temperature in reactor rose because there was no coolant • Operators inserted the control rods to slow the reaction • Control rods were made of graphite (carbon), which reacted with the extremely hot water to produce hydrogen gas which is explosive. Chemical Explosion (2H2O + C  2H2 + CO2) Blew the protective cover (4000ton) off the plant Radioactive isotopes released, reactor burned

  22. Fig.07.11

  23. Fig.07.12 Radioactive Fallout from Chernobyl~100 Hiroshima atom bomb equivalent

  24. Three Mile Island • March 1979 • Meltdown at Unit 2 reactor (Unit 1 still working today) • Caused by a slight malfunction and human error • No new nuclear power plants in United States since

  25. “The China Syndrome” • Movie that came out 12 days before T.M.I • Movie is based on a meltdown of a Nuclear Power Plant in California • “If that's true, then we came very close to the China Syndrome.  The number of people killed would depend on which way the wind was blowing. Render an area the size of Pennsylvania permanently uninhabitable.“

  26. More Recent • Fukoshima, Japan • March 11, 2011 • How bad was it / is it going to be?

  27. Can a Nuke Power Plant blow up like a Bomb? • SHORT Answer = NO Commercial Nuclear Power Plants needs 3-5% fissionable U-235 95-97% non-fissionable U-238 Bomb needs 90% fissionable U-235 10% U-238

  28. Radiation is dangerous since it imparts energy to the body • Penetrating ability • Alpha particle – a – large, helium nucleus • Does not travel through body very much, not terribly dangerous • Alpha emitter is Americium (#95), used in Smoke Detectors • Beta particle – b – an electron • Travels a little into body • Gamma energy – g – just energy • Can travel through entire body • Radon is an a and g emitter

  29. Radioactive Waste What do we do with it? First need to consider how long waste will be around and dangerous Half-life (t1/2) – time it takes for ½ material to decay Varies from isotope to isotope:234U t½ = 2.47x 105 yr238U t½ = 4.51x109 yr 123I t½ = 13.3hrs125I t½ = 60.2days

  30. Calculating half life • n = number of half lives • n = time waited / half life • Ending amount = Starting Amount / 2n • Example: If I have 10 pounds of radioactive material that has a half life of 150 years, and I wait 450 years, how much is still radioactive?

  31. Yucca Mountain Need a Place to Store the Radioactive Waste from: Dismantled Nuclear Weapons Spent Fuel from Nuclear Power Plants Problem: NIMBYNot In My Back Yard Where to put it? Serious efforts to use Yucca Mountain in NevadaNeeds: Geologically stable, Isolated from population, Isolated from water table, and rains

  32. Fig.07.26 Yucca Mountain

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