The stellar neutron capture cross sections of 1860S and 1870S are fundamental far the Re/Os cosmo-chronometer since they are defining the s-process abundance of 187 OS. Subtraction of the s-component from the solar 1870s abundance yields the radiogenic contribution to 187Os due to beta-decays of 187Re (t1/2 = 42.3 Gy) originating from r-process nucleosynthesis. The laboratory cross section of 187Os requires a significant correction for the effect of the low-lying excited state at 9.75 keV, which is strongly populated under stellar conditions. This reliability of the theoretical correction can be greatly improved by an experimental determination of the cross section far in¨elastic scattering to the 9.75 keV state. In this work, high resolution time-of-flight measurements of (n, gamma) cross sections of 186,187,188Os from 1 eV to 1 MeV performed at the CERN n_TOF facil¨ity 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 far the Re/Os clock are briefly discussed.
Experimental Challenges for the Re/Os Clock
Ventura, A.;
2006-06-25
Abstract
The stellar neutron capture cross sections of 1860S and 1870S are fundamental far the Re/Os cosmo-chronometer since they are defining the s-process abundance of 187 OS. Subtraction of the s-component from the solar 1870s abundance yields the radiogenic contribution to 187Os due to beta-decays of 187Re (t1/2 = 42.3 Gy) originating from r-process nucleosynthesis. The laboratory cross section of 187Os requires a significant correction for the effect of the low-lying excited state at 9.75 keV, which is strongly populated under stellar conditions. This reliability of the theoretical correction can be greatly improved by an experimental determination of the cross section far in¨elastic scattering to the 9.75 keV state. In this work, high resolution time-of-flight measurements of (n, gamma) cross sections of 186,187,188Os from 1 eV to 1 MeV performed at the CERN n_TOF facil¨ity 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 far the Re/Os clock are briefly discussed.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
