Search

We present a detailed account of neutron capture experiments of astrophysical relevance on 78,80,84,86Kr (n ,γ ) reactions at the border between weak and main s process. The experiments were performed with quasi-Maxwellian neutrons from the Liquid-Lithium Target (LiLiT) and the mA-proton beam at 1.93 MeV (2-3 kW) of the Soreq Applied Research Accelerator Facility (SARAF). The setup yields high-intensity ≈40 keV quasi-Maxwellian neutrons (3-5 ×1010 n /s) closely reproducing the conditions of s -process stellar nucleosynthesis. A sample of 100 mg of atmospheric, pre-nuclear-age Kr gas contained in a Ti spherical shell was activated in the LiLiT neutron field. The abundances of long-lived Kr isotopes (81,85 gKr) were measured by atom counting via atom trap trace analysis (ATTA) at Argonne National Laboratory and low-level counting (LLC) at University of Bern. This work is the first measurement of a nuclear cross section using atom counting via ATTA. The activities of short-lived Kr isotopes (79,85 m,87Kr) were measured by γ -decay counting with a high-purity germanium detector. Maxwellian-averaged cross sections for s -process thermal energies are extracted. By comparison to reference values, our nucleosynthesis network calculations show that the experimental cross sections have a strong impact on calculated abundances of krypton and neighboring nuclides, in some cases improving agreement between theory and observations.

The determination of the involved reaction cross sections is essential for the understanding of how the big bang nucleosynthesis and nuclear reactions in stars contribute to the observed abundances. One of those, which has not been measured so far, is the 10Be(n,γ) cross section. A 10BeO sample, provided by PSI Villigen, was irradiated in a cyclic activation at the TRIGA reactor in Mainz. The characteristic γ-rays following the decay of 11Be were measured using LaBr3 scintillation detectors. The thermal neutron cross section and the resonance integral were experimentally determined for the first time.

The determination of the involved reaction cross sections is essential for the understanding of how the big bang nucleosynthesis and nuclear reactions in stars contribute to the observed abundances. One of those, which has not been measured so far, is the $^{10}\mathrm{Be(n,\gamma)}$ cross section. A $^{10}\mathrm{BeO}$ sample, provided by PSI Villigen, was irradiated in a cyclic activation at the TRIGA reactor in Mainz. The characteristic $\gamma$-rays following the decay of $^{11}\mathrm{Be}$ were measured using $\mathrm{LaBr_3}$ scintillation detectors. The thermal neutron cross section and the resonance integral were experimentally determined for the first time.