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Applications of Nuclear Physics

Applications of Nuclear Physics. Fusion (How the sun works covered in Astro lectures) Fusion reactor Radioactive dating C dating Rb/Sr  age of the Earth. Physics of Nuclear Fusion. All reactions at low energy are suppressed by Coulomb barrier (cf a decay).

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Applications of Nuclear Physics

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  1. Applications of Nuclear Physics • Fusion • (How the sun works covered in Astro lectures) • Fusion reactor • Radioactive dating • C dating • Rb/Sr  age of the Earth Nuclear Physics Lectures

  2. Physics of Nuclear Fusion • All reactions at low energy are suppressed by Coulomb barrier (cf a decay). • Reaction rate: convolution of MB distribution and barrier penetration. Nuclear Physics Lectures

  3. Low Energy Fusion Cross Sections • Breit-Wigner (no-spin) • cf a decay theory, allow for QM tunnelling through Coulomb barrier Nuclear Physics Lectures

  4. Cross Sections (Continued) • Predicts cross section • Low energy approximation Nuclear Physics Lectures

  5. Example aC Theory explains rapid rise at very low energy Ignores multiple resonances! Nuclear Physics Lectures

  6. Fusion Rates • Consider reaction a+bX (a different from b) • Volume number density rarb • Cross section sab • Reaction rate/volume Nuclear Physics Lectures

  7. Maximum rate  minimum for f Nuclear Physics Lectures

  8. Fusion Rates pp reaction Look at exp[-f(E)] Function sharply peaked at E=E0 106exp[-f(E)] E (KeV) Nuclear Physics Lectures

  9. Fusion Rates • Most favourable rates for d-t reactions. • Peak at kBT~ 20 keV • Why? <vs(v)> m3s-1 kBT (keV) Nuclear Physics Lectures

  10. Fusion Reactors • Use deuterium + tritium: • Large energy release • Large cross-section at low energy • Deuterium abundant (0.015% of H). • Breed Tritium in Lithium blanket • . Nuclear Physics Lectures

  11. Fusion Reactors • Energy out > Energy in • Lawson criteria (assume kBT=20 keV). • number density D ions : r • Cross-section: s • Confinement time for plasma: tc • Energy released per fusion: Efusion Nuclear Physics Lectures

  12. Magnetic Confinement • Confine plasma with magnetic fields. • Toroidal field: ions spiral around field lines. • Poloidal fields: focus ions away from walls. • Heating: • RF power accelerates electrons • Current pulse causes further heating. Nuclear Physics Lectures

  13. Jet Nuclear Physics Lectures

  14. Nuclear Physics Lectures

  15. MAST Fusion Progress • Huge strides in physics, engineering, technology • JET: 16 MW of fusion power ~ equal to heating power. 21 MJ of fusion energy in one pulse • Ready to build ITER - the next generation, GigaWatt-scale • Scaling laws that fit data from existing tokamaks give confidence that ITER/power plants will achieve desired performance Fusion product p t (atm. sec) Temperature / 106 K Nuclear Physics Lectures

  16. AUG JET ITER Prediction of ITER performance JET Cross section of present EU D-shape tokamaks compared to the ITER project Nuclear Physics Lectures

  17. High Energy neutrons • Use n to make 3H in Li blanket • n damage to surrounding support structures ~ 10 dpa/yr • 2H +7Li  n + 2 4He Nuclear Physics Lectures

  18. Inertial Confinement Fusion Mirrors Very Big Laser D-T Pellet Nuclear Physics Lectures

  19. Inertial Confinement Fusion Nuclear Physics Lectures

  20. Radioactive Dating • C14/C12 for organic matter  age of dead trees etc. • Rb/Sr in rocks  age of earth. Nuclear Physics Lectures

  21. Carbon Dating • C14 produced by Cosmic rays (mainly neutrons) at the top of the atmosphere. • n N14 p C14 • C14 mixes in atmosphere and absorbed by plants/trees  constant ratio C14 / C12 . Ratio decreases when plant dies. t1/2=5700 years. • Either • Rate of C14 radioactive decays • Count C14 atoms in sample by Accelerator Mass Spectrometer. • Which is better? • Why won’t this work in the future? Nuclear Physics Lectures

  22. Carbon Dating Calibration Nuclear Physics Lectures

  23. How Old Is The Earth? • Rb87 Sr87: b decay t1/2=4.8 1010 yr • Assume no initial daughter nuclei  get age from ratio of daughter/parent now. Nuclear Physics Lectures

  24. Improved Calculation • Allow for initial daughters to be present. • Need another isotope of the daughter D’ which is stable and not a product of a radioactive decay chain. • Plot vs straight line fit  age and initial ratio. Nuclear Physics Lectures

  25. Age of Earth • Rb/Sr method • Stable isotope of daughter is Sr86 • Fit gives age of earth=4.53 109 years. Sr87/Sr86 1.0 4.0 Nuclear Physics Lectures Rb87/Sr86

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