We have measured the neutron capture cross sections of the stable magnesium isotopes 24,25,26 Mg in the energy range of interest to the s process using the neutron time-of-flight facility n_TOF at CERN. Capture events from a natural metal sample and from samples enriched in 25 Mg and 26 Mg were recorded using the total energy method based on C 6 2 H 6 detectors. Neutron resonance parameters were extracted by a simultaneous resonance shape analysis of the present capture data and existing transmission data on a natural isotopic sample. Maxwellian-averaged capture cross sections for the three isotopes were calculated up to thermal energies of 100 keV and their impact on s-process analyses was investigated. At 30 keV the new values of the stellar cross section for 24 Mg, 25 Mg, and 26 Mg are 3.8±0.2 mb, 4.1±0.6 mb, and 0.14±0.01 mb, respectively.

The neutron Time of Flight (n_TOF) facility at CERN is a source of a wide-range (1 eV

The n_TOF Collaboration has built and commissioned a high-performance detector for (n, gamma) measurements called the Total Absorption Calorimeter (TAC). The TAC was especially designed for measuring neutron capture cross-sections of low-mass and/or radioactive samples with the accuracy required for nuclear technology and stellar nucleosynthesis. We present a detailed description of the TAC and discuss its overall performance in terms of energy and time resolution, background discrimination, detection efficiency and neutron sensitivity. (C) 2009 Elsevier B.V. All rights reserved

A high-resolution measurement of the neutron-induced fission cross section of 234 U and 237 Np has been performed at the CERN Neutron Time-of-Flight facility. The cross sections have been determined in a wide energy range from 1 eV to 1 GeV using the evaluated 235 U cross section as reference. In these measurements the energy determination for the 234 U resonances could be improved, whereas previous discrepancies for the 237 Np resonances were confirmed. New cross-section data are provided for high neutron energies that go beyond the limits of prior evaluations, obtaining important differences in the case of 237 Np.

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