Lecture 16: Nuclear Physics Reviebelz/phys5110/lecture16.pdf · Midterm Exam Midterm on Monday...
Transcript of Lecture 16: Nuclear Physics Reviebelz/phys5110/lecture16.pdf · Midterm Exam Midterm on Monday...
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Lecture 16: Nuclear Physics Review
Physics 5110Spring Semester 2015
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Midterm Exam
● Midterm on Monday March 2nd
● Allowed resources:– One sheet of paper with notes, equations– Calculator, pencil or pen
● Subject matter: Nuclear physics– Short work out problems– Short answer
● Study homeworks, lecture examples, practice exams.
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Chapters/Topics
● Rutherford Scattering
● Nuclear Phenomenology
● Nuclear Models (liquid drop, shell)
● Radiation ()
● Applications (fission, fusion, decay)
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Ch 1: Rutherford Scattering
● Differential cross section d/d● Rutherford d/d● Possible short answer questions
– What is a differential cross section?– Explain how Rutherford scattering
demonstrates that there is a nucleus.– What are Mandelstam variables s,t,u, and
what do they signify physically?
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Sample Rutherford work-out problem
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Result from Lecture 2
● N0 = number of beam particles
● ,t = target density,thickness
● A0, A = Avogadro's #, Atomic mass
Hits recorded by detector
Differential Cross Section(physics)
Solid angle ofdetector
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Classical Scattering Theory(Fixed Target)
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Do the math...
● And after some arithmetic (homework)
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Ch 2: Nuclear Phenomenology
● Nuclear mass, size, spin, stability.● How do we know the above?● Possible short answer questions
– What is a form factor?– Explain how we can know the size of an
atomic nucleus.– What is binding energy, how is it
determined?
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Size of Nucleus
● Method suggested by diffraction of light
● Scatter particles of = h/p off of nucleus
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Ch 3: Nuclear Models
● Liquid Drop Model● Shell Model● Possible short answer questions
– Describe origin of term(s) in semi-empirical mass formula
– Describe role of spin-orbit interaction in the shell model
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Goal of Nuclear Models
● Can we model this curve?
● Can we make other predictions?
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The Semi-Empirical Mass Formula (Bethe-Weizaecker)
pairing
asymmetry
Coulomb
surface
volume
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“Pairing Term”
Phenomenological A dependence
● PP and NN are more strongly bound than PN.
● Introduce a term that has
– Greater BE for Zeven
Neven
.
– Zero BE for Zeven
Nodd
or Zodd
Neven
.
– Less BE for Zodd
Nodd
.
+ o-o− e-e0 o-e
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So the total splitting is given by:
→ splitting increases for larger l→ can produce “level crossing”→ hence desired shell structure!
Spin Orbit Effect in Shell Model
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Unpaired nucleons provide spin-parity assignment:
● Even-even nuclei → have zero spin (observed)
● Odd-Odd nuclei → can't predict :-( (we don't know how N-P will pair)
● Odd-Even (i.e. odd A) nuclei
– Determine which type of nucleons is odd-numbered
– Count odd nucleons to determine filled shells
– Spin-parity of last nucleon is that of nucleus
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Examples: Use shell model to estimate spin-parity and
magnetic dipole moment of...
● Tritium 3H1
● Lithium 7Li3
● Carbon 11C6
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Ch 4: Nuclear Radiation
● Alpha, Beta, Gamma Decays● Possible short answer questions
– Describe the role of “tunneling” in nuclear decays.
– Differentiate between the three types of “beta” decay.
– Describe how we infer the existence of neutrinos from beta decay
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Ch 5: Applications of Nuclear Physics
● Fission
● Fusion
● Radioactive decay law
● Possible short answer questions
– What is difference between spontaneous and induced fission?
– Interpret “Neutrons in Natural Uranium” plot.
– Explain the “moderator” in fission reactors.
– Why do we fuse light nuclei and “fiss” heavy nuclei to produce energy?
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Neutron interactions in Natural Uranium
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