Speaker
Marita Mosconi
(Forschungszentrum Karlsruhe GmbH (FZK))
Description
The stellar neutron capture cross sections of 186Os and 187Os are fundamental
for the Re/Os cosmo-chronometer for defining the s-process abundance of 187Os.
Subtraction of the s component from the solar 187Os abundance yields the
radiogenic contribution to 187Os due to the beta-decay of 187Re (t1/2=42.3 Gy)
since the onset of r-process nucleosynthesis. The laboratory cross section of 187Os
requires a significant correction for the effect of low-lying excited state at 9.75
keV, which is strongly populated under stellar conditions. This theoretical
correction can be improved by an experimental cross section for inelastic scattering
to the 9.75 keV state. High resolution time-of-flight measurements of (n,gamma) cross
sections of 186,187,188Os from 1 eV to 1 MeV at CERN n_TOF facility are reported. The
inferred stellar cross sections differ from previously recommended values. In
addition, the inelastic scattering cross section has been measured at 30 keV neutron
energy via time-of-flight at the Karlsruhe 3.7 MV Van de Graaff. The
implications of these results for the Re/Os clock are discussed
Author
Marita Mosconi
(Forschungszentrum Karlsruhe GmbH (FZK))
Co-authors
Dr
Alberto Mengoni
(International Atomic Energy Agency, Vienna)
Dr
Franz Käppeler
(Forschungszentrum Karlsruhe GmbH (FZK))
Mrs
Kaori Fujii
(Istituto Nazionale di Fisica Nucleare, Trieste)
Dr
Michael Heil
(Forschungszentrum Karlsruhe GmbH (FZK))
Dr
Ralf Plag
(Forschungszentrum Karlsruhe GmbH (FZK))
Prof.
Roberto Gallino
(Universita' di Torino)
