Speaker
Description
It is well ascertained since the late '50, that the vast majority of the elements above the iron peak are synthesized in stars, via sequences of neutron captures and β-decays. Among the nucleosynthesis mechanisms, the slow (s-)process represents one of the better known and is very effective into modelling the stellar evolution. Thanks to the high accuracy of the nuclear data available in the major libraries, the s-process models can predict the final element abundances from iron to lead with high precision.
An accurate measurement of the 140Ce(n,γ) energy dependent cross section has been performed at the n_TOF facility at CERN. This measurement was motivated by the significant discrepancy in the cerium abundance observed in the globular cluster M22 and the value predicted by theoretical stellar models [1].
The experimental apparatus was based on a highly enriched 140Ce sample and on C6D6 liquid scintillators to detect the γ produced following the neutron capture events. The experimental data up to 65 keV allowed us to resolve 81 neutron resonances, which provides the largest contribution to the MACS at the temperature of interest for the s-process. The n_TOF data show large discrepancies compared to the cross section reported in the major nuclear data libraries, as shown in Fig.1 (Resonance Shape Analysis of a p-wave resonance: n_TOF data presents large disceprancies compared to both ENDF/B-VIII and JENDL-4.0 libraries.).
The robustness of the n_TOF results is ensured by a good agreement with the MACS measured by activation by Käppeler et al. [2] at kT = 30 keV. At lower temperatures, high discrepancy with respect to the values provided by KADoNiS has been observed. The experimental results of the 140Ce(n,γ) cross section and the astrophysical impact of the new MACS on the s-process modelling in the Ba-Ce-Nd region will be presented.
[1] O. Straniero, S. Cristallo, L. Piersanti. Heavy elements in globular clusters: the role of asymptotic giant branch stars, ApJ 2014, 785, 77.
[2] F. Käppeler et al. Neutron capture cross sections of the cerium isotopes for s- and p-process studies, Phys. Rev. C 1996, 53, 1397.