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NE 301 - Introduction to Nuclear Science Spring 2012

NE 301 - Introduction to Nuclear Science Spring 2012. Classroom Session 2: Natural Radioactivity Chart of the Nuclides Nuclear Stability (Binding Energy, BE) Radioactive Decay Types Radioactive Decay and Growth Isotopes and Decay Diagrams Nuclear Reactions Energy of nuclear reactions

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NE 301 - Introduction to Nuclear Science Spring 2012

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  1. NE 301 - Introduction to Nuclear ScienceSpring 2012 Classroom Session 2: Natural Radioactivity Chart of the Nuclides Nuclear Stability (Binding Energy, BE) Radioactive Decay Types Radioactive Decay and Growth Isotopes and Decay Diagrams Nuclear Reactions Energy of nuclear reactions Neutron Cross Sections Activation Calculations

  2. Prelude… • Please bring clickers to class. • Please bring calculators. • Get in pairs/groups, feel free to talk across tables. • Time on task please. I want everybody working to get answers.

  3. Radioactivity in Nature • Discovered in 1896 by Henri Becquerel • Using photographic plates • Notice: no natural sensors for radiation • Marie Curie: differences between radioactivity of Uranium and Uranium minerals • Discovered Polonium then Radium (both 1898) • Main radioactive minerals are:

  4. Main Radioactive Minerals

  5. Main Naturally Occurring Isotopes: Trivia: 14C production: • ~22,000 at/s/m2 of earth surface 3H production: • ~2,500 at/s/m2 • Global Planetary Equilibrium Inventory of: 63 tons of 14C 3.5 kg of 3H

  6. A Bit of History… Filling the Periodic Table • The Periodic Table of the Elements • 1869 by Dmitri Mendeleev • Elements Known: • 1 – H to 83 – Bi. Plus U and Th. • Some stable elements later (Hf -1922, Re- 1925) • Natural Unstable Elements: • Po, Rn, Fr, Ra, Ac, and Pa (mainly by Curies) • Artificial Elements • 43-Tc , 61-Pm , 85-At, and Transuranics (Np, Pu, Am, etc)

  7. Isotopes… • 40 kinds of atoms with different half-lives were found • Problem: Only 13 spots available in the Periodic Table • Frederick Soddy in 1913: • Isotopes = “In the Same Place” • Nobel Prize 1921 • It was later discovered that stable atoms also can have isotopes (e.g. Sn has 10 stable and 18 unstable ones).

  8. Atomic and Nuclear Nomenclature • X element symbol (H, He, Na, Xe, U, etc.) represents the number of charges in the nucleus (thus electrons, thus chemical behavior). • A= Mass number = protons + neutrons = Nucleons. • Z= atomic number = protons. • X and Z are redundant and normally we only write AX. e.g. 235U, 16O, 3H, 14C

  9. Nuclides Atoms differing by atomic number of mass number • Radionuclide: • Unstable nuclide • Table of nuclides Provide accurate mass of each nuclide

  10. Chart of the Nuclides

  11. Chart of the Nuclides Isobars Isotopes Z Isotones N

  12. Trivia: Nuclides known: Found in Nature: Main Nat. Radioactive: Produced by cosmic rays: • ~2800 • 258 Stable • 25 with Z<80 reported radioactive (7 not confirmed) • 235U, 238U, 232Th and decay families. • 14C, 10Be, 7Be, 3H

  13. Nuclear Isomers • Certain Nuclides with different physical properties • Half-lives • Modes of decay • Metastable states of the same nuclide • Either decay by -emission • Transmute to other nuclides (,  decay, etc) • Suffix “m” next to A. (i.e. 60mCo, 99mTc)

  14. Download • RadDecay, by Charles Hacker • Play with it: • How to find nuclides • Half-life • Understand Decay products • ’s • ’s • ’s • X-Rays • electrons

  15. Nuclear Stability

  16. Stability of Nuclei – General Observations • In general, nuclei with an even number of protons or neutrons are more stable • As the protons increase electromagnetic forces increase and more neutrons are needed to provide attractive nuclear force to keep the nucleus together • Certain Z or N numbers are particular stable (Higher BE) • 2, 8, 20, 28, 50, 82, 126 Magic Numbers

  17. Stability with Even or Odd Z

  18. Stability with Even or Odd N Even Z, Even N = 159 Even Z, Odd N = 53 Odd Z, Even N = 50 Odd Z, Odd N = 4

  19. Let’s do some accounting… • For example: • Mass of Oxygen Atom: Mp=1.007276 amu Mn=1.008665 amu Me=5.48e-4 amu 1 amu = 931.49 MeV Mass Defect = Binding Energy (BE)

  20. Nuclear Stability and Binding Energy (BE) • Higher BE = Higher Stability • Compare BE of 12C and 14C: • To understand stability and radioactive decay, please calculate BE for the following ISOBARS (A=73): 73Zn, 73Ga, 73Ge, 73As, 73Se, 73Br, 73Kr Everybody!

  21. Isobars = A

  22. Notice radioactive decay stabilizes atoms: • Question: Do fission products normally have - or + decay?

  23. Chart of the Nuclides Z=N Z i.e. Fission products are neutron rich N

  24. Another Example: Notice several stable possibilities

  25. If we graph naturally occurring atoms… Fission Fusion

  26. Reaction reactants and products If E is positive: reaction exothermic releases energy If E is negative, reaction endothermic requires energy Endoergic and exoergic is sometimes used Reaction Energetics A + B  C + D + E

  27. Please remember… BALANCE! Before starting to work

  28. Balancing Reactions nucleons  1 +16 = 16+1 Charges (+)  0 + 8 = 7 + 1 (-)  -0 -8 = -7 -0  e- missing 0 1 So in reality the reaction is: Calculating Q…

  29. Q-value for the reaction is: Using atomic mass tables: Endothermic reaction. Only a few fission neutrons can do it

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