Abstract
Activations with neutrons in the keV energy range were routinely performed at the Karlsruhe Institute of Technology (KIT) in Germany in order to simulate stellar conditions for neutron-capture cross sections. A quasi-Maxwell-Boltzmann neutron spectrum of kT = 25 keV, being of interest for the astrophysical s-process, was produced by the 7Li(p,n) reaction utilizing a 1912 keV proton beam at the Karlsruhe Van de Graaff accelerator. Activated samples resulting in long-lived nuclear reaction products with half-lives in the order of yr 100 Myr were analyzed by Accelerator Mass Spectrometry (AMS). Comparison of the obtained reaction cross sections to literature data from previous Time-of-Flight (ToF) measurements showed that the selected AMS data are systematically lower than the ToF data. To investigate this discrepancy, 54Fe(n,γ)55Fe and 35Cl(n,γ)36Cl reaction cross sections were newly measured at the Frankfurt Neutron Source (FRANZ) in Germany. To complement the existing data, an additional neutron activation of 54Fe and 35Cl at a proton energy of 2 MeV was performed. The results will give implications for the stellar environment at kT = 90 keV, reaching the not yet experimentally explored high-energy s-process range. AMS measurements of the activated samples are scheduled.
Highlights
The astrophysical slow neutron-capture process (s-process) is responsible for the production of about half of the heavy elements above iron in late stellar burning phases
Subsequent Accelerator Mass Spectrometry (AMS) measurements of the chemicallyprocessed samples will be performed at the 14 UD tandem accelerator at the Heavy Ion Accelerator Facility (HIAF) at the Australian National University in Canberra [27] and at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) in Germany [28, 29]
Subsequent single-atom counting via AMS is scheduled at the Heavy Ion Accelerator Facility at the Australian National University in Canberra and Helmholtz-Zentrum DresdenRossendorf in Germany
Summary
The astrophysical slow neutron-capture process (s-process) is responsible for the production of about half of the heavy elements above iron in late stellar burning phases. As particles in stellar environment follow the Maxwell-Boltzmann distribution, the corresponding cross section is referred to as Maxwellian-Averaged Cross Section (MACS) [1, 2]. MACS can be experimentally determined measuring the total energy of prompt gammas following irradiation with a pulsed high-intensity neutron beam with a wide energy range. The MACS can be calculated by folding the measured energy-dependent cross sections with an appropriate Maxwell-Boltzmann distribution. The activation technique [3,4,5] offers a complementary approach to determine MACS. A sample is irradiated with a quasi-Maxwell-Boltzmann neutron
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