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Chapter 30

Chapter 30. Nuclear Reactions. Nuclear Reactions. Chemical reactions between atoms and molecules involve only the orbital electrons Nuclear reactions involve changes in nuclei Radioactivity is a natural nuclear reaction Most nuclear reactions are induced by collisions between particles

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Chapter 30

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  1. Chapter 30 Nuclear Reactions

  2. Nuclear Reactions • Chemical reactions between atoms and molecules involve only the orbital electrons • Nuclear reactions involve changes in nuclei • Radioactivity is a natural nuclear reaction • Most nuclear reactions are induced by collisions between particles • Particle accelerators

  3. Nuclear Reactions • Induced nuclear reactions usually just involve reorganization of the neutrons and protons • No *poof* • Same numbers of ho-hos and twinkies, just different lunch packets

  4. Nuclear Reactions • Q-value—energy-mass conversion involved in the reaction • m = (initial masses) – (final masses) • E = mc2 • Endoergic—energy is absorbed in reaction • Q value is negative • Threshold energy—minimum energy needed to initiate reaction • Usually KE of incoming particle • Exoergic—energy is released in reaction • Q value is positive

  5. Nuclear Fission • Large molecules will sometimes break apart due to collisions • Usually collisions with neutrons • Total mass of daughter nuclei is smaller than parent nucleus • Energy released, E = mc2 About 1 MeV released

  6. Nuclear Fission

  7. Nuclear Fission

  8. Nuclear Fission • Critical mass—minimum mass of fissionable material needed for a sustained reaction • Natural Uranium is only 0.7 % fissionable 235U, 99.3% 238U • More purity needed for sustained reaction • 3-5% pure for power generating reactors • 99% for nuclear weapons

  9. Nuclear Fission • Fuel rods—Small uranium pellets packed together in tubes • Reactor core is the collection of fuel rods • Usually about 200 rods • Place them in water, and the fission reaction heats the water • Control rods—neutron absorbing material placed between the fuel rods to regulate the reaction • Scramming—suddenly, fully deploying all control rods to completely stop the fission reaction • How a Nuclear Power plant works

  10. Nuclear Fission • The bomb • Multiple fragments (smaller than critical mass) brought together to form a piece larger than critical mass • 1.5 – 23 % of the uranium actually fissions • Still, wow • How Nuclear Bombs Work

  11. Nuclear Fusion • Smaller elements brought together to form larger elements • Total mass of the daughter nucleus is smaller than the total mass of the parent nuclei • E = mc2 • Much more energy released than in fission reactions • Very high molecular KE (temperatures) needed to force nuclei together

  12. Nuclear Fusion • Deuterium (2H) and Tritium (3H) fuse to form various isotopes of Helium 17.6 MeV released

  13. Nuclear Fusion • Fusion Bombs • Called thermonuclear bombs • Fission bomb trigger to create heat and pressure needed for fusion

  14. Nuclear Fusion • Fusion Power • That’s what fuels the stars • Heat supplied by gravitational pressure • Difficult to contain and control because of the high heat needed • Magnetically contained in rings called tokamaks • Little concern for meltdown, as fusion reactions need high heat to continue • They’d just fizzle if it broke

  15. Nuclear Fusion

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