Measurement of the stellar cross sections for the reactions 9Be(n,?)10Be and 13C(n,?) 14C via AMS

Abstract

We started a series of experiments, aiming at obtaining neutron-capture cross sections from measurements of the production of both long-lived nuclides 10Be and 14C, in the energy region of interest for astrophysical applications. Neutron-rich scenarios lead to the production of the long-lived radionuclides 10Be (t1/2 = 1.51 Myr) and 14C (t1/2 = 5730 yr) via neutron-capture reactions on 9Be and 13C, respectively. Data for both neutron-capture reactions are sparse and disagree in the astrophysical relevant energy region between 10 and 250 keV. Since (n,γ) cross sections in this mass and energy range are expected to be very small (some tens of νbarn), the combination of the activation technique and accelerator mass spectrometry (AMS) offers the powerful experimental approach which is necessary for such investigations. Beryllium oxide and enriched 13C graphite samples have been irradiated in a quasi-stellar neutron spectrum of kT = 25 keV at Forschungszentrum Karlsruhe. The subsequent AMS measurements were performed at the VERA (Vienna Environmental Research Accelerator) laboratory. The first AMS results confirm the expected low cross sections of about 10 νbarn for both reactions.