Behavior of Nuclear Reaction Networks

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Behavior of Nuclear Reaction Networks

• Brad Meyer
• Clemson University

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QSE Quasi-statistical equilibrium
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(n,gamma)-(gamma,n) equilibrium
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For a given Z
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Parameters

• Ye
• net number of electrons per nucleon
• fraction of all nucleons that are protons
• E.g., Ye 0.5 means equal numbers of neuetron
  and protons. Ye 0 means all neutrons. Ye1
  means all protons.

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Parameters (cont.)

• Entropy per nucleon
• Degrees of freedom per nucleon
• In units of Boltzmanns constant kB
• E.g., all free nucleons s/kB about 3
• E.g., all nucleons in 56Fe s/kB about 3/56
• s/kB gt 20 typically means a lot of photons and
  electron-positron pairs around.

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Parameters (cont.)

• Timescale tau
• Density expansion efolding timescale
• Typically milliseconds to seconds

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The Alpha-Rich Freezeout

• Explosive Silicon Burning

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The r-Process (I)
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BBN
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The r-Process (II)
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Assembling 4He from n,p

• Early reaction sequences like p(n,g)d(n,g)t(d,n)4
  He
• Later catalysis by reaction cycles like
  56Fe(n,g)57Fe(n,g)58Fe(p,g)59Co(p,4He)56Fe

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New FITS files to play with

• R process files rprocess.html
• Big bang calculations bbang1.fits (s/k2x1010),
  bbang2.fits (s/k2x109), bbang3.fits (s/k2x1011)

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Take home message I

• Steady states, steady states, steady states

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Take home message II

• Constrained equilibria, constrained equilibria,
  constrained equilibria