Shell model applications in nuclear
astrophysics
Karlheinz Langanke
GSI Helmholtzzentrum Darmstadt
Technische Universität Darmstadt
Shell model and nuclear structure – Ischia, May 14, 2014
In honor of Aldo Covello
Closer look on
• electron capture in presupernova phase
(nuclear composition A ~ 60)
- electron capture during collapse
(nuclear composition A > 65)
- r-process in neutron star mergers
Supernova: schematic view
courtesy:
R. Diehl
Electron capture: Lab vs Stars
Capture is dominated by Gamow-Teller transitions
During collapse, electrons are described by Fermi-Dirac distribution
with chemical potentials of order a few MeV
Parent nuclei are described by thermal ensemble
Calculating stellar capture rates
data KVI Groningen
Capture on nuclei in mass range A~45-65 calculated by large-scale shell model
Capture rates are noticeably smaller than assumed before!
Consequences of capture rates
Heger
Woosley
Martinez
Pinedo
shell model rates for Fe-Ni nuclei
slower by order of magnitude
important changes in
collapse trajectory
Experiment vs shell model
Cole, Zegers et al., PRC 86 (2012) 015809
Iron-nickel mass range under control
With increasing density, less sensitivity to details of GT distribution
-> models less sophisticated than shell model suffice, e.g. QRPA
Abundances in Type Ia‘s
Type Ia‘s have produced about half of the
abundance of nickel-iron range nuclei in
the Universe
Modern electron capture rates solve inconstency
problem in Type Ia supernova abundance production
Martinez-Pinedo, Thielemann
Abundance distribution during
collapse
Electron captures drive nuclear composition towards neutron-rich
unstable nuclei
Unblocking GT for nuclei with
neutron numbers N>40
In Independent Particle Model, GT are Pauli-blocked for N>40
In reality, blocking does not occur due to correlations and finite T.
Calculations of rates by SMMC/RPA model.
Experimental GT distributions
courtesy Dieter Frekers
Neutron occupancies
Data from transfer reactions: J.P Schiffer and collaborators
Convergence with truncation level
Cross-shell correlations converge slowly. Hence, models like
thermofield dynamics model or finite temperature QRPA, which
consider only 2p-2h correlations, do not suffice. (Zhi et al.)
Consequences of shell model
rates
Janka, Rampp, Martinez-Pinedo
Making Gold!
Nature
vs
Humans
Old stars in galactic halo have the same
r-process abundances as the solar system
for A>130, but not below.
two distinct r-process sites?
Johann Friedrich Böttger, Alchemist
Inventor of European White China
In Meissen, Germany
The R-Process
•
•
•
•
•
Courtesy: K.-L. Kratz
Masses
Half lives
Neutron capture rates
Fission
Neutrino reactions
Potential r-process sites
Neutrino-driven wind from a
nascent neutron star in a
supernova explosion
(Woosley et al.)
simulations show that conditions
allow only for production upto
second r-process peak
Neutron star mergers
Freiburghaus et al.
Trajectories and reheating
After initial adiabatic expansion
and cooling, the nuclear reactions
(mainly beta decays) lead to a
reheating of the ejected matter.
The temperatures are high enough
to establish an
(n,gamma)<>(gamma,n)
equilibrium. Due to the extreme
neutron densities, the r-process path
runs through nuclei not far from the
neutron dripline.
A. Bauswein, H.-Th. Janka
Abundance evolution in ns merger
third peak produced like in
classical r-process
(neutron captures, beta decays)
second peak produced by fission
yields
neutron captures after freeze-out
lead peak produced by late
alpha decays
Mendoza, Martinez-Pinedo...
Dependence of half lives
Eichler, Thielemann et al.
faster half lives shift the peak back in mass number
due to faster consumption of neutrons
Half lives around N=126
shell model:
forbidden transitions
important
(Suzuki et al. Zhi et al.)
data in neighborhood of N=126 show
that half-lives are faster than believed
(T. Nieto, KH. Schmidt et al.)
faster matter flow through N=126
waiting points,
faster consumption of neutrons
faster fission cycling
abundances and mass models
Mendoza, Martinez-Pinedo et al.
quite unsensitive to mass models, fission cycling dominates
ns merger -> robust abundance pattern, like in old stars?
Next-Generation Isotope Facilities
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RIBF contribution: masses
FAIR
Impact of nuclear half-lives
Impact of nuclear half-lives
on r-process abundances
Knowing the half-lives we will
constrain the dynamics of the
supernova explosion
The RIB Chance: New Horizons