Speaker
Sebastian Müller
(Institut fuer Kernphysik, TU Darmstadt)
Description
Photodissociation cross sections play an important role in our understanding of
nucleosynthesis in the mass region above A > 60. The bulk of these heavy nuclei is
produced by neutron capture reactions during the s- and r-process.
The so-called branching points of the s-process have typical half-lives of the order
of a few days up to a few hundred years. The direct measurement of neutron capture
cross sections of the short-living is not feasible. However, some of the long-living
ones were measured successfully [1,2].
We try to constrain theoretical predictions of the capture cross section by measuring
the inverse ($\gamma$,n) cross section directly above the neutron threshold. A
current result, the cross section of $^{186}$Re(n,$\gamma$) will be shown and its
influence on the Re/Os-chronometer will be discussed [3].
About neutron deficient nuclei with masses A > 60 cannot be produced by neutron
capture reactionS. These so-called p-nuclei are produced by photodisintegration
reactions during the p-process. The p-process takes place at temperatures of about
2.5GK. At this temperature the photons stemming from the thermal photon bath induce
($\gamma$,n), ($\gamma$,$\alpha$), and ($\gamma$,p) reactions. We can emulate
thermal photon spectra in the needed energy range to deduce directly the ground state
reaction rates [4]. We will show recent results for neutron deficient nuclei
with Z > 78 [5].
One of the remaining puzzles is the abundance of the neutron deficient Molybdenum
isotopes. These abundances are underestimated by all network calculations by at least
one order of magnitude. We measured the coulomb dissociation cross section of
$^{92,93,94,100}$Mo at the LAND setup at GSI. This cross section can be converted
into a photodissociation cross section. For comparison, the photodisscociation cross
section of $^{100}$Mo will be measured at the S-DALINAC using real photons.
The last part of this presentation will be about the status of the
quasi-monochromatic photon source NEPTUN at the S-DALINAC. The high resolution photon
tagger NEPTUM at the S-DALINAC is designed to measure ($\gamma$,n) cross sections
with an energy resolution of about 0.25% in the energy range between 8 MeV and 20 MeV.
[1] K. Wisshak, F. Voss, F. Käppeler, M. Krtcka, S. Raman, A. Mengoni, and R.
Gallino, Phys. Rev. C 73, 015802 (2006)
[2] U. Abbondanno et al. Report CERN-SL-2002-053 ECT, CERN (2003)
[3] S. Müller, A. Kretschmer, K. Sonnabend, A. Zilges and D. Galaviz, Phys. Rev. C,
in press
[4] P. Mohr, K. Vogt, M. Babilon, J. Enders, T. Hartmann, C. Hutter, T. Rauscher, S.
Volz and A. Zilges Phys. Lett B 488, 127 (2000)
[5] K. Sonnabend, K. Vogt, D. Galaviz, S. Müller and A. Zilges, Phys. Rev. C 70,
035802 (2004)
Author
Sebastian Müller
(Institut fuer Kernphysik, TU Darmstadt)
Co-authors
Prof.
Andreas Zilges
(Institut fuer Kernphysik, TU Darmstadt)
Mr
Jens Hasper
(Institut fuer Kernphysik, TU Darmstadt)
Mr
Kai Lindenberg
(Institut fuer Kernphysik, TU Darmstadt)
Dr
Kerstin Sonnabend
(Institut fuer Kernphysik, TU Darmstadt)
Ms
Linda Kern
(Institut fuer Kernphysik, TU Darmstadt)
