Nucleosynthesis of Intermediate- Mass and Heavy Nuclei

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					        Nucleosynthesis of Intermediate-
                   Mass and Heavy Nuclei
     Friedrich-Karl Thielemann
     Department of Physics and
                Astronomy
         University of Basel


  with many collaborators over the
                  years
Basel: T. Rauscher, M. Liebendörfer,
  S. Rosswog, C. Freiburghaus, F.
  Brach-witz, C. Fröhlich, D. Mocelj
Darmstadt: G. Martinez-Pinedo, K.
  Langanke,..
Mainz: K.-L. Kratz, B. Pfeiffer, K.
  Farouqi
Oak Ridge: R. Hix,..
    Nucleosynthesis of intermediate-mass and
                 heavy nuclei

●   Nucleosynthesis Processes after B2FH
●   Stellar Burning and Final Stages
●   Explosive Burning
●   Equilibria and Freeze-out Effects
●   Astrophysical Sites
●   Existing Problems
●   New Processes Required?
Stellar Burning Stages
Stellar Burning Stages
Stellar Burning Stages
 Global Chemical (=Nuclear
Statistical) Equilibrium (NSE)
                  Explosive Burning




Ne   C                                          Ne     Si

typical explosive burning process timescale order of seconds: fusion
reactions (He, C, O) density dependent (He quadratic, C,O linear)
photodisintegrations (Ne, Si) not density dependent
                  Explosive Si-Burning




                            5

Explosive Burning above a critical temperature destroys (photodisintegrates) all
nuclei and (re-)builds them up during the expansion. Dependent on density, the full
NSE is maintained and leads to only Fe-group nuclei (normal freeze-out) or the
reactions linking 4He to C and beyond freeze out earlier (alpha-rich freeze-out).
     Explosive Si-burning
initially only 28Si, fully burned, finally alpha-
rich freeze-out
 visualization: B.S. Meyer
              Quasi-Equilibrium (QSE)
                            full NSE is not attained, but
                            there exist equilibrium groups
                            around 28Si, 56Ni and n,p,4He,
                            which are separated by slow
                            reactions




Sample Calculations from
● B.S. Meyer and

● Hix and Thielemann
                   alpha-rich freeze-out




              increasing entropy

                                                 increasing entropy
       Thielemann et al. (1996)
alpha-rich freeze-out occurs at high temperatures and/or low densities and is a
function of entropy S in radiation-dominated matter
● it leads to the enhancement of “alpha-elements”

● and also to the extension of the Fe-group to higher masses (56Ni to 64Ge and

for very high entropies up to A=80)
  “Historical”      Present Understanding
Burning Processes
                    ● H-Burning
     (B2FH)         ● He-Burning

●   H-Burning       ● expl. C, Ne, O-Burning, incomplete

                      Si-Burning
●   He-Burning      ● explosive Si-Burning

                    - about 70% normal freeze-out with
●   alpha-Process      Ye=0.42-47, about 30% alpha-rich
                       freeze-out with Ye=0.5
●   e-Process       ● s-Process (core and shell He-burning,

●   s-Process        neutrons from alpha-induced reactions on
                    22
                      Ne and 13C)
●   r-Process       ● r-Process (see below)

                    ● p-Process (see below)

●   p-Process       ● x-Process (light elements D, Li, Be, B

                     [big bang, cosmic ray spallation and
●   x-Process         neutrino nucleosynthesis])
 The Heavy Elements
Solar abundances (Anders & Grevesse)
         (from Anders & Grevesse)




  s-process
  r-process
  p-process
              s-, r- and p-Process




F. Käppeler

                              P. Möller
p-Process (explosive Ne-burning = “photon spallation”)




                                  Arnould      and   Goriely
                                  (2003)problems          in
                                  underproducing Mo, Ru and
                                  a number of heavier p-
                                  process isotopes!!
           Working of the r-Process
●   (complete) Explosive Si-Burning
●   1. (very) high entropy alpha-rich (charged-particle) freeze-out
        with upper equilibrium extending up to A=80
    - quasi-equilibria in isotopic chains (chemical quilibrium for
        neutron captures and photodisintegrations) with maxima at
        specific neutron separation energies Sn
     - neutron/seed(A=80) ratio and Sn of r-process path
       dependent on entropy and Ye

●   2. low entropies and normal freeze-out with very low Ye,
      leading also to large n/seed ratios

    - Sn function of Ye
n/seed ratios as function of S and Ye




              Freiburghaus et al. (1999)
                                              nn=1020
                                                                                                       r-Process paths for nn=1020, 1023 and 1026
                                                                                                                                        K.-L. Kratz
                                                                                                                                                                                         82        84   86   88   90   92   94

                                                                                                                             Ba
                                                                                                                               Cs
                                                                                                                             Xe
                                                                                                                                I
                                                                                                                             Te
                                                                                                                               Sb
  Sn
In
  Cd
Ag
  Pd
Rh
  Ru
Tc
   Mo
Nb
   Zr                                                                                                                                                                                                             nn=1023
Y
   Sr
Rb
   Kr
Br

As
  Se                                                                                                                                                       n =10n
                                                                                                                                                                              26

  Ge
Ga
   Zn
Cu
   Ni
Co
   Fe      42       44      46        48      50       52       54       56      58        60      62       64        66       68       70       72       74        76       78       80      82


 Z N                                       „waiting-point“ isotopes for nn=1020, 1023 and1026
Individual Superpositions of Entropy Components
  Farouqi (2005), above S=270-280 fission back-cycling sets in




                                                    Pb
                                                           Th

                                                                 U
Processes in the Nuclear Chart




                                 H. Schatz
        Astrophysical Sites
                       Hertzsprung-Russell Diagram
                       of Stellar Evol-ution from
                       Iben, showing as end stages

                       ●   white dwarfs

                       and
                       ●   (core collapse) supernovae


main sequence
Type Ia Supernovae from Accretion in Binary Stellar Systems
     Back of the Envelope SN Ia




P. Höflich
            Neutronization via electron capture
           (high Fermi energies at central densities)
     56
      Ni

54
     Fe, 58Ni

 56
      Fe

50
 Ti,54Cr



           (a) Test for influence of new shell model electron capture rates (LMP)
           (b) Test for burning front propagation speed
Ignition density determines Ye and
neutron-richness of (60-70% of) Fe-group

                                results of explosive
                                C, Ne, O and Si-
                                burning:
                                Fe-group to alpha-
                                elements 2/1-3/1

                                SNe Ia dominate
                                Fe-group, over-
                                abundances by
                                more than factor 2
                                not permitted

                                central density
                                <4 109 gcm-3
Future 3D Models

          Travaglio, Reinecke,
          Hillebrandt, Thielemann (2004)

          hydrodynamic instabilities
          determine propagation of
          burning

          consistent treatment needed
          instead of parametrized spherical
          propagation,
          MPA Garching, U. Chicago,
          U. Texas/Florida
          Role of Sne Ia and Sne II in galactic evolution
           stellar surface abundances as witness of gas composition during formation
                                             Prantzos (2005)




[el/Fe]




                                                                       onset of Sne Ia at
                                                                       [Fe/H]=-1 dominate
                                                                       Fe-production, alpha-
                                                                       elements dominated
                                                                       by Sne II.
Core Collapse Supernovae from
        Massive Stars
   Neutrino-driven Core Collapse
            Supernovae




A. Mezzacappa
    “Faking” multi-D hydro with neutrinos




                               We make use of 1D models and
Liebendörfer et al. (2004)     reduction factors on neutrino
code AGILE/BOLTZTRAN           scattering or enlargement factors in
with full Boltzmann neutrino   neutrino absorption in order to obtain
transport                      typical explosion energies
   Nucleosynthesis problems in “induced”
      piston or thermal bomb models
utilized up to present to obtain explosive nucleosynthesis yields
                with induced explosion energies of 1051 erg




prior results of Thielemann, Nomoto, Woosley, Chieffi .. made use of initial stellar structure (and
Ye!) when inducing artificial explosion. This neglects the effect of the explosion mechanism on
the innermost zones, causes strange overproductions of Ni isotopes and does not go mucch
beyond Ni!
     In exploding models matter in innermost
   ejected zones becomes proton-rich (Ye>0.5)
if the neutrino flux is sufficiant
(scales with 1/r2)! :




                                     Fröhlich et al. (2006a)
                                     A: neutrino scattering cross sections
                                     scaled (%)
                                     B: neutrino absorption cross sections
                                     scaled (factor)
Improved Fe-group composition
                          Models with Ye>0.5 lead to an
                          alpha-rich freeze-out with
                          remaining protons which can
                          be captured similar to an rp-
                          process. This ends at 64Ge, due
                          to (low) densities and a long
                          beta-decay half-life (decaying
                          to 64Zn).
                          This effect improves the Fe-
                          group composition in general
                          and extends it to Cu and Zn!

Fröhlich et al. (2006a)
                          νp-process




                                  A new process, which could solve some
Fröhlich et al. (2006b);          observational problems of Sr, Y, Zr in early
also strong overabundances can    galactic evolution and the problem of light p-
be obtained up to Sr and beyond   process nuclei.
(light p-process nuclei)          Anti-neutrino capture on protons provides
                                  always a small background of neutrons which
                                  can mimic beta-decay via (n,p)-reactions.
       Variations in explosion dynamics and neutrino luminosity
                                Fröhlich et al. (2006b), see also Pruet et al.
                                (2006)




permits to explain on the one
hand that in some cases only
large overabundances of Sr
are found, on the other hand
early abundances of Sr,Y, Zr
as well as possible p-process
nuclei up to A=120
Observations of Sr, Y, Zr in low- metallicity stars
                                    Travaglio et al. (2004)




Frebel et al. (2005)
large variations in Sr between
different low-metallicity stars
                                  Need for early Sr,Y,Zr before
                                  onset of s-process
    Observational Constraints on r-Process Sites




     Cowan and Sneden
                                         “rare” event, which must be related
apparently uniform abundances above      to massive stars due to “early”
Z=56 (and up to Z=82?) -> “unique”       appearance           at         low
astrophysical event which nevertheless   metallicities(behaves similar to SN
consists of a superposition of ejected   II products like O, but with much
mass zones                               larger scatter)
      What is the site of the r-process?
      from S. Rosswog                  from H.-T. Janka




NS Mergers, problems: ejection   SN neutrino wind, problems:
too late in galactic evolution   high enough entropies attained?
   Superposition of 5 entropies

                N=50
                                 N=82
                                                       N=126              Th, U


                                                                                       r-process
                                                                                    chronometers

  „weak“
 r-process




Thesis K. Farouqi 2005: entropies up to about 280, higher entropies lead to fission back-
cycling! Low (high) entropies produce essentially an alpha-rich freeze-out around A=80
without neutrons left and leave abundance features which do not fit the A=80 peak.
However from meteorites as well as low metallicity stars we know that another process
(weak r-process) must be responsible here.
Finding high entropies seemed extremely difficilt in
      neutrino wind (Thompson et al. 2001)!




       Only very massive neutron stars seemed to come close to conditions
       (entropies) which can produce the third peak!!!
Fission Cycling in Neutron Star Mergers




   Freiburghaus et al. (1999) with simplified symmetric fission
   for nuclei with A>250, complete lack of nuclei below A=115
Self-consistent explosion models absolutely needed!

                               fallback onto neutron
        increasing explosion   star: supernova and
        energy: neutron star   black hole
        and supernova
                                                                        Liebendörfer et al.
                                                       direct black     (2006), explosions
                                                       hole formation   via changed neu-
                                                                        trino properties




  only with models which provide the explosion energy and the properties of the
  innermost ejected matter we can give a clear prediction of the Fe-group
  composition and possible r-process ejecta.
  Most recent models of the Garching, Arizona, Los Alamos and Basel groups
  (in 2D) see apparently high enough entropies for the r-process in the fall back.

				
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posted:10/17/2011
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