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n_TOF Collaboration(Fujii, K. et al), Domingo-Pardo, C., & Tain, J. L. (2010). Neutron physics of the Re/Os clock. III. Resonance analyses and stellar (n, gamma) cross sections of Os-186,Os-187,Os-188. Phys. Rev. C, 82(1), 015804–18pp.
Abstract: Neutron resonance analyses have been performed for the capture cross sections of Os-186, Os-187, and Os-188 measured at the n_TOF facility at CERN. Resonance parameters have been extracted up to 5, 3, and 8 keV, respectively, using the SAMMY code for a full R-matrix fit of the capture yields. From these results average resonance parameters were derived by a statistical analysis to provide a comprehensive experimental basis for modeling of the stellar neutron capture rates of these isotopes in terms of the Hauser-Feshbach statistical model. Consistent calculations for the capture and inelastic reaction channels are crucial for the evaluation of stellar enhancement factors to correct the Maxwellian averaged cross sections obtained from experimental data for the effect of thermally populated excited states. These factors have been calculated for the full temperature range of current scenarios of s-process nucleosynthesis using the combined information of the experimental data in the region of resolved resonances and in the continuum. The consequences of this analysis for the s-process component of the Os-187 abundance and the related impact on the evaluation of the time duration of galactic nucleosynthesis via the Re/Os cosmochronometer are discussed.
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n_TOF Collaboration(Massimi, C. et al.), Domingo-Pardo, C., Giubrone, G., & Tain, J. L. (2017). Neutron spectroscopy of Mg-26 states: Constraining the stellar neutron source Ne-22(alpha, n)Mg-25. Phys. Lett. B, 768, 1–6.
Abstract: This work reports on accurate, high-resolution measurements of the Mg-25(n, gamma)Mg-26 and Mg-25(n, tot) cross sections in the neutron energy range from thermal to about 300 keV, leading to a significantly improved Mg-25(n, gamma)Mg-26 parametrization. The relevant resonances for n+Mg-25 were characterized from a combined R-matrix analysis of the experimental data. This resulted in an unambiguous spin/parity assignment of the corresponding excited states in Mg-26. With this information experimental upper limits of the reaction rates for Ne-22(alpha, n)Mg-25 and Ne-22(alpha, gamma)Mg-26 were established, potentially leading to a significantly higher (alpha, n)/(alpha, gamma) ratio than previously evaluated. The impact of these results has been studied for stellar models in the mass range 2 to 25 M-circle dot. (C) 2017 The Author(s). Published by Elsevier B.V.
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n_TOF Collaboration, Kappeler, F., Mengoni, A., Mosconi, M., Fujii, K., Heil, M., et al. (2011). Neutron Studies for Dating the Universe. J. Korean Phys. Soc., 59(2), 2094–2099.
Abstract: The neutron capture cross sections of (186)Os and (187)Os are of key importance for defining the 8-process abundance of (187)Os at the formation of the solar system. This quantity can be used to determine the radiogenic abundance component of (187)Os from the decay of (187)Re (t(1/2) = 41.2 Gyr) and to infer the time-duration of the nucleosynthesis in our galaxy (Re/Os cosmochronometer). The neutron capture cross sections of (186)Os, (187)Os, and (188)Os have been measured at the CERN nTOF facility from 1 eV to 1 MeV, covering the entire energy range of astrophysical interest. From these data Maxwellian averaged capture cross sections have been calculated with uncertainties between 3.3 and 4.7%. Additional information was obtained by measuring the inelastic scattering cross section of (187)Os at the Karlsruhe 3.7 MV Van de Graaff accelerator and by neutron resonance analyses of the nTOF capture data to establish a comprehensive experimental basis for the Hauser-Feshbach statistical model. Consistent I-IF calculations for the capture and inelastic reaction channels were performed to determine the stellar enhancement factors, which are required to correct the Maxwellian averaged cross sections for the effect of thermally populated excited states. The consequences of this analysis for the s-process component of the (187)Os abundance and the related impact on the evaluation of the time-duration of Galactic nucleosynthesis via the Re/Os cosmo-chronometer are discussed.
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n_TOF Collaboration(Belloni, F. et al), Domingo-Pardo, C., & Tain, J. L. (2012). Neutron-induced fission cross section measurement of U-233, Am-241 and Am-243 in the energy range 0.5 MeV <= E-n <= 20 MeV at n_TOF at CERN. Phys. Scr., T150, 014005–4pp.
Abstract: Neutron-induced fission cross section measurements of U-233, Am-243 and Am-241 relative to U-235 have been carried out at the neutron time-of-flight facility n_TOF at CERN. A fast ionization chamber has been employed. All samples were located in the same detector; therefore the studied elements and the reference U-235 target are subject to the same neutron beam.
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n_TOF Collaboration(Diakaki, M. et al), Domingo-Pardo, C., & Tain, J. L. (2016). Neutron-induced fission cross section of Np-237 in the keV to MeV range at the CERN n_TOF facility. Phys. Rev. C, 93(3), 034614–12pp.
Abstract: The neutron-induced fission cross section of Np-237 was experimentally determined at the high-resolution and high-intensity facility n_TOF, at CERN, in the energy range 100 keV to 9 MeV, using the U-235(n, f) and U-238(n, f) cross section standards below and above 2 MeV, respectively. A fast ionization chamber was used in order to detect the fission fragments from the reactions and the targets were characterized as far as their mass and homogeneity are concerned by means of a spectroscopy and Rutherford backscattering spectroscopy respectively. Theoretical calculations within the Hauser-Feshbach formalism have been performed, employing the EMPIRE code, and the model parameters were tuned in order to successfully reproduce the experimental fission cross-sectional data and simultaneously all the competing reaction channels.
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