L. Ferrant

Measurements of neutron capture cross-sections for ADS-related studies

Capture cross-sections on several isotopes relevant to accelerator driven systems for energy production and nuclear waste transmutation, and to stellar nucleosynthesis can be studied at the innovative neutron time of flight facility (n_TOF) at CERN. The experimental apparatus is based on a low-mass Si-based flux monitor and a set of C6D6 liquid scintillator detectors. The accurate reconstruction of the cross-sections relies on the pulse height weighting function technique. The set-up used in the measurements is here described. The first results on reference isotopes, Au, Ag and Fe, used to verify the accuracy of the method are presented. � 2003 Elsevier B.V. All rights reserved.

Capture Cross Section Measurements of 186,187,188Os at n_TOF: The Resolved Resonance Region

The neutron capture cross sections of 186,187,188Os have been measured at the CERN neutron time-of-flight facility, n TOF, in the neutron energy range from 1 eV up to 1MeV. In this contribution, we report the results of the analysis of the resolved resonance region (RRR). Resonance parameters have been extracted from a full R-matrix fit of the capture yields with the SAMMY code. A statistical analysis has been performed and the related average resonance parameters are derived. This information is crucial for a complete understanding and modeling in terms of the Hauser-Feshbach statistical model of the capture and inelastic reaction channels, required for the evaluation of the stellar reaction rates of these isotopes. Maxwellian average cross sections for the range of temperatures relevant for s-process nucleosynthesis have been derived from the combined information of the experimental data in the resolved and unresolved resonance regions. A brief account of the implications of this analysis in the estimation of the s-process component of the 187Os abundance and the related impact on the estimates of the time-duration of the galactic nucleosynthesis through the Re/Os clock is given.

Fission of Actinides Induced by Neutrons at nTOF

The neutron‐induced fission cross sections of 233U, 234U, 232Th, 237Np, 209Bi, natPb have been measured on the nTOF facility at CERN, which allows an accurate energy measurement owing to the long path. Parallel plate avalanche counters were used to detect the 2 fission fragments in coincidence. This method allows an efficient discrimination of fission reactions among other types of reactions especially at high energies, and it is well suited for the very large energy range available at nTOF. The case of 234U will be used as an example of the quality of the data obtained in these measurements.