Equilibrium means all allowed states are equally likely

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Equilibrium means all allowed states are equally
likely!

• Paradox of statistical mechanics toss out
  nearly all information about a system but get a
  good description of it!

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System looks like the most probable state

• Sk log(multiplicity)
• so maximize the multiplicity, or, equivalently,
  the entropy

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Most abundant species is the fittest
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Fitness of Nuclear Species

• Binding energy per nucleon
• Neutron richness
• Availability of excited states (increased
  multiplicity)

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Binding Energy B(Z,A)

• B(Z,A) Z mpc2 (A-Z) mnc2 - m(Z,A)c2
• Energy to completely to take the nucleus apart
  into its constituent nucleons
• Mass excess (in MeV)

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Abundances

• Define abundance per nucleon Y of species and
  mass fraction X

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Neutron Richness

• Quantified by Ye

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Partition Function

• Partition function G accounts for the
  multiplicity of a species

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Alfred Russel Wallace
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