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NE 301 - Introduction to Nuclear Science Spring 2012

NE 301 - Introduction to Nuclear Science Spring 2012. Classroom Session 5: Isotopes and Decay Diagrams Nuclear Reactions Energy of nuclear reactions Neutron Cross Sections Activation Calculations Radioactive Decay and Growth. Reminder. Load TurningPoint Reset slides Load List.

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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 5: Isotopes and Decay Diagrams Nuclear Reactions Energy of nuclear reactions Neutron Cross Sections Activation Calculations Radioactive Decay and Growth

  2. Reminder • Load TurningPoint • Reset slides • Load List

  3. -, + produce three products: • Cannot say energy of  • Neutrinos by Fermi (1933) • We only can say maximum energy of  • Page 98-Shultis

  4. Binary Nuclear Reactions • Binary = 2 reactants (many times 2 products too) • Most important type of nuclear reaction • Most elements produced by binary rxns. in stars • Nomenclature: Light nuclide usually projectile Light Product Heavy Product Heavy nuclide usually target

  5. For Binary Reactions: x +X  Y + y • x is a projectile with KE (Ex). X is a target stationary nucleus EX=0 simplification

  6. A 5.5 MeV particle is incident on Li causing 7Li(,n)10B. What is the KE of neutron scattered 30o?

  7. A 5.5 MeV particle is incident on Li causing 7Li(,n)10B. What is the KE of neutron scattered 30o? • 0 MeV • 0.31 MeV • 1.31 MeV • 2.31 MeV • 3.31 MeV • 5.5 MeV

  8. FIRST BALANCE THE EQUATION!!! 7Li(alpha,n)10B Endothermic Rxn Neutron Energy = 1.31MeV What would be the neutron energy if incident alpha particle is 1MeV instead? Can’t happen…

  9. Solution exists only if • Potential “” Factors • Q<0 • Heavy projectiles (mY-mx<0) • Large scattering angles Cos <0 • Big enough Ex can guarantee • Physical meaning: Threshold Energy Argument of root >0

  10. Kinematic Threshold (only if Q<0) • Arises from conservation of: • Energy • Linear momentum (Details are in the textbook) • In most nuclear reactions (mi’s>Q), the kinematic threshold simplifies to: ONLY FOR Q<0 i.e. endothermic rxns.

  11. What is the kinematic threshold for: 7Li(,n)10B ? • 0.4 MeV • 1.4 MeV • 2.4 MeV • 3.4 MeV • 4.4 MeV

  12. What is the kinematic threshold for: 13C(d,t)12C • -1.5 MeV • 0 MeV • 1.5 MeV • 3 MeV • 9.6 MeV Remember: Kinematic Threshold only for Endothermic Reactions

  13. Remember: Kinematic Threshold only for Endothermic Reactions • Balance. Then: • (13.003355+2.014102-12-3.016049)*931.494 • Q=1.31154 MeV Exothermic = Kinematic Threshold is 0 MeV

  14. Coulomb Barrier Threshold (fig. 3.9) Coulombic Threshold • ONLY when the incident nuclide is charged • All nuclides are positive • Projectile needs energy to overcome electrostatic repulsion Binding Energy NOT for incident NEUTRONS nor ’s Engineering Equation. MeV units already worked out (don’t worry)

  15. What is the coulomb barrier threshold for: 7Li(,n)10B ? • 1 MeV • 2 MeV • 3 MeV • 4 MeV • 5 MeV

  16. Clicker Answer

  17. What is the coulomb barrier threshold for: 14N(n,)11B ? • 0 MeV • 1 MeV • 2 MeV • 3 MeV • 0.98 x Q MeV

  18. Overall Threshold Energy • Neutral Incident particle=No Coulomb Barrier. • Q>0 = No Kinetic Threshold • Charged particles and Q<0 = both thresholds apply, and: Do NOT add – Use BIGGEST of the two

  19. What would be the minimum KE of Products? – think about it! Min. Kinetic Energy of the products is: Energy produced in the reaction Minimum required energy of the incident particle

  20. What is the threshold for the 7Li(,n)10B nuclear reaction? • 0 MeV • 2.06 MeV • 4.4 MeV • 6.46 MeV 30 Remember: Threshold is minimum energy the incident particle has to have

  21. What is the threshold of 14C(p,n)14N ?And Minimum KE of the Products ? • 3.1 MeV and 3.74 MeV • 2.1 MeV and 2.74 MeV • 3.1 MeV and 2.74 MeV • 2.1 MeV and 3.74 MeV • 0 MeV and 6 MeV

  22. 14C(p,n)14N

  23. Neutron Scattering • First Type: • Scattering reactions • Elastic scattering (Q=0) • Inelastic scattering (Q<0)

  24. N Scattering Kinematics It is still a binary rxn. So eq. still applies, but • Solving for the scattering angle: Simplifies to:

  25. What is the energy of a 5MeV neutron after it is elastically scattered 30o by a 10B atom? • 1.9 MeV • 2.9 MeV • 3.9 MeV • 4.9 MeV • 5.9 MeV Hint: for elastic collisions only “+” matters

  26. Notice it is an elastic collision: • Q=0

  27. Accelerator in Columbia (8.4 MeV d) How many of these could happen?

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