Abstract.A series of measurements of neutron induced fission cross section of various TRU isotopes have been performed at the CERN n TOF spallation neutron facility, in the energy range from thermal to nearly 250 MeV. The experimental apparatus consists in a fast ionization chamber (FIC), used as a fission fragment detector with a high efficiency. Good discrimination between alphas and fission fragments can be obtained with a simple amplitude threshold. In order to allow the monitoring of the neutron beam and to extract the n TOF neutron flux, the well known cross section of the 235 U(n,f) reaction, considered as a fission standard, has been used. Preliminary results for the cross section are shown for some selected isotopes such as 235 U, 233 U and 245 Cm in the energy range from 0.050 eV to about 2 MeV.

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Abstract. Neutron resonance spectroscopy plays an important role in the investigation of neutron induced reaction cross sections and nuclear structure in the MeV excitation range. Neutron time-of-flight facilities are the most used installations to explore neutron resonances. In this paper we describe the basic features of neutron resonance spectroscopy together with recent results from the time-of-flight facility n TOF at CERN.

Abstract. The neutron capture cross sections of 186,187,188 Os have been measured at the CERN neutron time-of-flight facility, n TOF, in the neutron energy range from 1 eV up to 1 MeV. 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 187 Os abundance and the related impact on the estimates of the time-duration of the galactic nucleosynthesis through the Re/Os clock is given.

Abstract. We have measured the neutron capture and fission cross section of 233 U at the neutron time-of-flight facility n TOF at CERN in the energy range from 1 eV to 1 MeV with high accuracy by using a high performance 4π BaF 2 Total Absorption Calorimeter (TAC) as a detection device. The method, based on the TAC energy response study, allowing to disentangle between γ's originating from fission and capture will be presented as well as the first very preliminary results.