Towards stellar neutron capture cross section measurements at the Soreq Applied Research Accelerator Facility

  M. Tessler [1]  ,  G. Feinberg [1,2]  ,  M. Friedman [1]  ,  A. Shor [2]  ,  M. Paul [1]  ,  D. Berkovits [2]  ,  D. Cohen [1]  ,  Y. Eisen [2]  ,  G. Giorginis [3]  ,  S. Halfon [1,2]  ,  A. Krasa [3]  ,  A. Plompen [3]  
[1] [1] Racah Institute of Physics, The Hebrew University of Jerusalem, Jerusalem, Israel, 91904
[2] [2] Nuclear Physics and Engineering Division, Soreq NRC, Yavne, Israel, 81800
[3] [3] EC-JRC-IRMM, Retieseweg 111, 2440 Geel, Belgium

High-intensity neutron sources are needed for measurements of stellar neutron capture cross sections. The 7Li(p,n)7Be reaction is a well-known source for neutron production in the keV region. For a proton incident energy of 1.912 MeV (about 30 keV above the reaction threshold), neutrons emitted from a thick Li target, have an energy distribution similar to that of a flux of neutrons at a temperature of kBT ~ 25 keV, which is the relevant temperature for some of the nucleosynthesis s-process sites. The spectrum of neutrons emitted by the 7Li(p,n) reaction on a thick 7Li target was studied in detail using the IRMM-Geel van de Graaff accelerator [1] and a detailed Monte-Carlo simulation program (SimLiT) was written for design and analysis of experiments [2]. An intense 7Li(p,n)7Be neutron source based on a Liquid-Lithium Target (LiLiT) was developed at the high-intensity proton superconducting linear accelerator of the Soreq Applied Research Accelerator Facility (SARAF). Phase I of the SARAF accelerator will be capable of delivering proton and deuteron beams with currents up to 2 mA up to about 3 MeV. The intensity of the neutron source expected from the LiLiT target on the basis of the SimLiT code is 2×1010 n/s per mA of incident proton beam with a quasi-Maxwellian spectrum for kBT ~ 28 keV. Stellar neutron cross sections are important for understanding nucleo-synthesis of heavy elements (A>60) in stars. We plan to use the activation method, using the SARAF - LiLiT experimental setup,  to measure stellar neutron capture cross sections of selected nuclides in the weak slow (s-) process (60<A<90) region (Fe to Br). In this region, it was shown that individual cross section strongly impact on the whole subsequent weak s-process path [3]. We also plan to measure the 209Bi(n,g)210g,mBi  reaction cross section, which is the end of the chain for the s-process of nucleo-synthesis in red giant stars, with the same method. This work is supported by the Pazi Foundation and the German-Israel Foundation (GIF).

[1] G. Feinberg et al., Phys. Rev. C 85, 055810  (2012)
[2] M. Friedman et al., Nucl. Instr. Meth. Phys. Res. A 698, 117 (2013)
[3] H. Nassar et al., Phys. Rev Lett.  94, 092504 (2005)