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We report on recent experiments at the Soreq Applied Research Accelerator Facility Liquid-Lithium Target (SARAF-LiLiT) laboratory dedicated to the study of  s -process neutron capture reactions. The kW-power proton beam at 1.92 MeV (1-2 mA) from SARAF Phase I yields high-intensity 30 keV quasi-Maxwellian neutrons (3-5×10 10  n/s). The high neutron intensity enables Maxwellian averaged cross sections (MACS) measurements of low-abundance or radioactive targets. Neutron capture reactions on the important  s -process branching points  147 Pm and  171 Tm were investigated by activation in the LiLiT neutron beam and  γ -measurements of their decay products. MACS values at 30 keV extracted from the experimental spectrum-averaged cross sections are obtained and will be discussed. The Kr region, at the border between the so-called weak and strong  s -process was also investigated. Atom Trap Trace Analysis (ATTA) was used for the first time for the measurement of a nuclear reaction cross section. After activation in the quasi-Maxwellian neutron flux at SARAF-LiLiT, isotopic ratios were determined for  81 Kr(230 ky)/ 80 Kr and  85 g  Kr(10.8 y)/ 84 Kr. The latter ratio was confirmed both by low-level β counting and  γ  spectrometry. The shorter-lived capture products  79,85 m ,87 Kr were detected by  γ  -spectrometry and the corresponding neutron-capture MACS of the respective target nuclei  78,84,86 Kr were determined. The MACS of the  80 Kr(n,  γ ) 81 Kr and  84 Kr(n,  γ ) 85 g  Kr reactions are still under study. The partial MACS leading to  85 m  Kr(4.5 h) measured in this experiment has interesting implications since this state decays preferentially by  γ  decay (79%) to  85 Rb on a faster time scale than does  85 g  Kr and behaves thus as an  s -process branching point.

Study of Astrophysical s-Process Neutron Capture Reactions at the High-Intensity SARAF-LiLiT Neutron Source