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Lesson 5

Lesson 5. Fundamental Aspects of Nuclear Structure. Fundamental Forces of Nature. Exchange Particles and Force Carriers. Forces occur through the notion of the virtual exchange of bosons that are force carriers.

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Lesson 5

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  1. Lesson 5 Fundamental Aspects of Nuclear Structure

  2. Fundamental Forces of Nature

  3. Exchange Particles and Force Carriers Forces occur through the notion of the virtual exchange of bosons that are force carriers “Virtual” means we can “violate” conservation of energy by an amount ΔE for a time Δt given by the Heisenberg Uncertainty Principle by emitting a photon (boson) The distance travelled by this photon is R where R=cΔt For particles with mass

  4. Electromagnetic force • Virtual exchange of photons

  5. Nuclear Force • Virtual exchange of particles of mass m

  6. What does this mean?

  7. Let’s focus on the strong or nuclear force. What are the properties of the “strong” force? 1. It is “short” range, R < 1.4 fm Evidence for this Saturation of forces, nearest neighbor interaction, B.E.(avA) 2. It is attractive with a repulsive core (quark volume)

  8. Nuclear Force • Not spherically symmetric (deuteron quadrupole moment), has symmetric central component and asymmetric tensor component. • Spin dependent (deuteron ground state is triplet, singlet state is unbound)

  9. Nuclear potential (simple square well model)

  10. Woods-Saxon Potential

  11. Woods-Saxon Potential

  12. Other potentials of note

  13. Other potentials of note

  14. Table 5-1 Charge independence of nuclear forces The nuclear force between a neutron and a proton is the same as the force between two protons or two neutrons.

  15. Isospin Consider that the neutron and the proton are just two states of the nucleon. Consider further that these two states are labeled by a quantum number, T, called isospin. For the nucleon, T=1/2. There are two projections of T in isospace, T3=+1/2 (proton) and T3=-1/2 (neutron) For a nucleus containing Z protons and N neutrons, T3=(Z-N)/2.

  16. Example Consider the A=10 isobars, 10Be, 10Band 10C. 10Be and 10Chave T3=±1. Thus they must be part of an isospinmultiplet, T=1. In 10B, T3=0, but there must be a state with T=1. This state is called the isobaric analog of the ground states of 10Be and 10C.

  17. Quarks Properties of Quarks Spin ½ Charge ±1/3, ±2/3 6 types (flavors) Size < 10-18m

  18. The neutron The proton

  19. Back to “Fundamental Particles”“Classification of Particles” Using Spin For Classification Fermions(e,p,n) ½ integer spin No two particles may occupy the same quantum state. Bosons(photon) Integer spin Do not obey Pauli exclusion principle (Animation)

  20. Types of Fermions Fermionic Hadrons interact via the strong interaction—p,n Leptons Do not interact via the strong interaction--e

  21. Types of Hadrons Baryons (Fermionic Hadrons) Composed of three quarks like the proton or neutron They are fermions Strongly interacting Mesons (Bosonic Hadrons) Composed of quark/anti-quark pairs. They are bosons Strongly interacting

  22. Examples of Fermions

  23. Lepton conservation The number of leptons is conserved in nuclear processes L=1 for each particle, L=-1 for each antiparticle

  24. Examples of Bosons

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