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Introduction to Nuclear Astrophysics II

Introduction to Nuclear Astrophysics II. Richard H Cyburt. Solar System Abundances . Also called… Cosmic abundances Solar abundances Standard abundances Measured by 2 methods Meteoritic abundances Solar Photospheric abundances. Abundance Normalizations.

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Introduction to Nuclear Astrophysics II

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  1. Introduction to Nuclear Astrophysics II Richard H Cyburt

  2. Solar System Abundances • Also called… • Cosmic abundances • Solar abundances • Standard abundances • Measured by 2 methods • Meteoritic abundances • Solar Photospheric abundances

  3. Abundance Normalizations • Meteoritic abundances cited with a normalization such that N(Si) = 106 atoms • Photospheric abundances determined relative to Hydrogen

  4. Abundance Measures • Mass fraction: Xi = ri/rB (r = mass density) • Si Xi = 1 • Mole fraction: Yi = ni/nB (n = number density) • Xi = Mi/MuYi = AiYi • El/H = ni/nH = Ni/NH (N = column density) • [El/H] = log10(El/H) – log10(El/H)solar

  5. Nuclear Masses • Z = proton number or atomic number • N = neutron number • A = mass number = N+Z • M(A,Z) = Amu + D(A,Z) • D(A,Z) is the mass excess • M(A,Z) = ZmH + Nmn – B(A,Z) • B(A,Z) is the binding energy http://www.nndc.bnl.gov/amdc/

  6. Q-values REACTION: A+B -> C+D • Q-value is energy released in reaction • Q = MA + MB – MC – MD • For 3He(a,g)7Be Q = 1.5861 MeV

  7. Why are Masses important? • Energy release powers stars & explosions • Gamma-rays can be seen….. COMPTEL all-sky 26Al 1.809 MeV map

  8. Reaction cross section • Cross section is the effective area of interaction for a given reaction. • Gross Estimate: s = pa2 • What is the typical interaction size? • Only 2 length-scales • Size of nuclide, R • de Broglie wavelength, k-1 ~E-1/2 • s = p(k-1+R)2

  9. What’s a better estimate? • One that includes the probability for penetrating the nucleus….. • For n-induced: P ~ kR • For Z-induced: P ~ (2phkR)exp(-2ph) • h = Z1Z2a2c/v ~ E-1/2

  10. S-factor • s=E-1S(E)exp(-2ph) • Combines de Broglie and penetration • Pulls out geometric terms, leaving only nuclear

  11. Cross Section vs S-factor From NNDC website: www.nndc.bnl.gov Cyburt & Davids 2008

  12. Resonances • s ~ GiGf/[ (E-Er)2 + (Gtot/2)2 ] • Gi = 2g2P(E) • g2 = reduced width • Gg ~ Eg3 for E1 transitions • Basics of R-matrix…. (see Descouvemont & Baye 2010)

  13. Reaction Rates • Rate = sv • Thermonuclear rate = thermal average

  14. The JINA REACLIB Databasehttp://groups.nscl.msu.edu/jina/reaclib/db/ MySQL database PHP web-interface Uptodate rxn rates Continuously updated Rate version tracking Includes expt & thry Cyburt et al. The Astrophysical Journal: Supplement Series 189 (2010) 240

  15. NUCDATALIBhttp://groups.nscl.msu.edu/jina/nucldatalib/ MySQL database PHP web-interface Nuclide properties Masses Partition functions Ground state spins Store existing evaluations Build libraries w/ evaluations Includes expt & thry

  16. The JINA Virtual Journals http://groups.nscl.msu.edu/jina/journals/jinavj/ http://groups.nscl.msu.edu/jina/journals/seguevj/ • Accessible online • ~30 journals • Published weekly • Categorization • Email notification • JINA VJ • broad NA scope • SEGUE VJ • More obs-based Cyburt et al. D-Lib Magazine January/February 2010 Volume 16, Number 1/2.

  17. Other Online Tools Computational Astrophysics Data Evaluation/Dissemination NuGrid [http://forum.astro.keele.ac.uk:8080/nugrid] MESA [http://mesa.sourceforge.net/] www.webnucleo.org National Nuclear Data Center [www.nndc.bnl.gov] Oak Ridge National Lab’s www.nucastrodata.org

  18. Conclusions • Nuclear Astrophysics is Diverse Field • It requires nuclear input for calculations • Masses • Structure • Reactions • Cross talk between fields is most important

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