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Nuclear Reactions

Nuclear Reactions. Natural Transmutation. 1 term on reactant side o riginal isotope (naturally radioactive) 2 terms on product side e mitted p article n ew Isotope. Happens all by itself (spontaneous) Not affected by anything in environment. Natural Transmutation.

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Nuclear Reactions

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  1. Nuclear Reactions

  2. Natural Transmutation 1 term on reactant side original isotope (naturally radioactive) 2 terms on product side emitted particle new Isotope Happens all by itself(spontaneous) Not affected by anything in environment

  3. Natural Transmutation 16N 0e + 16O 8 -1 7 2 terms on product side 1 term on reactant side

  4. Artificial Transmutation cause to happen: smash particles into one another 2 terms on reactant side original Isotope (non-radioactive) particle that hits it neutron, proton, or -particle product side: usually 2 terms

  5. Artificial Transmutation 27Al + 4He  30P + 1n 15 0 “bullet” - thing hits isotope 13 2 original isotope or target nucleus

  6. Artificial Transmutation 27Al + 4He 30P + 1n 2 15 0 13 1 2 8 7 2 35 0 33 0 17 all these equations have2 reactants! 14N + 4He 17O + 1H 75As + 4He 78Br + 1n 37Cl + 1n 38Cl 17

  7. Bombarding with protons or  protons & -particles have positive charge and mass do some damage when hit target nucleus must be accelerated to high speeds to overcome repulsive forces between nucleus & particle (both are +)

  8. What is an accelerator? vacuum chamber (usually long pipe) surrounded by vacuum pumps, magnets, radio-frequency cavities, high voltage instruments & electronic circuits inside pipe particles are accelerated to very high speeds then smashed into each other

  9. FissionReaction • splitting heavy nucleus into 2 lighter nuclei • requires critical mass of fissionable isotope • controlled: nuclear reactor • uncontrolled: bomb

  10. Fission reactant side: 2 terms 1 heavy isotope (examples: U-235 or Pu-239) bombarding particle – usually a neutron product side: at least 2 terms 2 medium-weight isotopes 1 or more neutrons huge amount energy released Fission = Division

  11. Fission 235U + 1n 91Kr + 142Ba + 31n + energy 56 0 36 92 235U + 1n 72Zn + 160Sm + 41n + energy 30 0 92 0 62 0 more than 200 different product isotopes identified from fission of U-235 small amount of mass is converted to energy according to E = mc2

  12. Fusion reactant side has 2 small nuclei: H + H; H + He; He + He product side: 1 nucleus (slightly larger; still small) and maybe a particle source of sun’s energy 2 nuclei unite 2H + 3H 4He + 1n + energy 0 2 1 1

  13. CERN • 27 kilometer ring • particles travel just below speed • of light • 10 hrs: particles make 400 • million revolutions of ring

  14. 4 miles in circumference! FermiLab

  15. Balancing Nuclear Equations

  16. Nuclear Equations - tasks • identify type (4 types): • natural transmutation • artificial transmutation • fission • fusion • balance to find unknown term

  17. Natural Transmutation – ID • 1 term on reactant side • starting isotope • 2 terms on product side • ending isotope & emitted particle • type of particle emitted characteristic of isotope – Table N

  18. Nuclear Equations • to balance: use conservation of both atomic number & mass number • mass number = left superscript • atomic number = left subscript

  19. Balancing Nuclear Equations 16N 0e + 16O -1 7 8 conservation of mass number:16 = 0 + 16 conservation of atomic number:7 = -1 + 8

  20. Writing Equations • write equation for decay of Thorium-232 • use Table N to find decay mode: α • write initial equation: 232Th 4He +X 90 2 figure out what element it turned into

  21. What’s under the hat? Little cats X, Y, & Z!

  22. Write an equation for the α decay of Th-232 232Th 4He + YX what’s X? 95 2 Z

  23. so Y = 228 232 = 4 + Y Y Z 2 232Th 4He + X 90 conservation of mass number: sum mass numbers on left side must = sum mass numbers on right side

  24. 2 90 Z 90 = 2 + Z so Z = 88 232Th 4He + 228X conservation of atomic number: sum of atomic numbers on left side must = sum of atomic numbers on right side

  25. 90 2 88 X = Ra use PT to find X: 232Th 4He + 228Ra 90 2 88 232Th 4He + 228X

  26. Radioactive Decay Series • sometimes 1 transmutation isn’t enough to achieve stability • some radioisotopes go through several changes before achieve stability (no longer radioactive)

  27. radioactive decay series: Th-232 transmuting to Pb-208

  28. β-14C 14N + 0e 6 7 -1 beta β+18F  18O + 0e 8 +1 positron 9

  29. How does the mass number or atomic number change in α,β or γ decay? • go to Table N: • find isotope that decays by α or βdecay • write equation • see how mass number (or atomic number) changes • 22688Ra 42 + X so X has to be 22286X • αdecay of Ra-226: • mass number decreases by 4 • atomic number decreases by 2

  30. So how do you know if an element is radioactive or not? the key is the proton to neutron ratio

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