Neutron cross sections for carbon and oxygen from new R-matrix analyses of the 13,14C and 17O systems
Theoretical Division, Los Alamos National Laboratory, Los Alamos NM 87545, USA
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Published online: 13 September 2017
We report the latest results from R-matrix analyses of reactions in the 13,14C and 17O systems that are of interest in reactor applications and nuclear astrophysics. These were done in order to provide separate cross sections for the stable isotopes (12,13C) of natural carbon, and to contribute improved cross sections for 16O to the CIELO project. Although particular attention was paid to the data in the standards region (<2 MeV) for the carbon isotopes, and to the low-energy region for n+16O, the analyses extend to several MeV neutron energy for all the systems. The fits to the data included are generally quite good, in keeping with the unitary constraints of R-matrix theory. The cross sections for 12,13C give results for natural carbon that are close to the previous evaluation by Fu et al. at energies below 1 MeV. Above that energy, the deviations become larger, especially near the narrow resonances. The thermal cross section for 16O is at the upper end of the range of recommended values, in excellent agreement with a high-precision measurement by Schneider. At higher energies, the 17O analysis follows in great detail high-resolution measurements of the total cross section, and agrees quite well with the 13C(α,n)16O cross section measurement of Bair and Haas at roughly their original normalization scale. We will discuss the implications of these new evaluations for critical benchmarks and astrophysical applications.
© The Authors, published by EDP Sciences, 2017
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