Measurement of the 209Bi(n,γ)210Big cross section and updated s-process analysis of the Pb/Bi regionS. Bisterzo1, 2, F. Käppeler2, R. Gallino1, M. Heil3, C. Domingo-Pardo2, C. Vockenhuber4 and A. Wallner
1 Dipartimento di Fisica Generale, Università di Torino, via P. Giuria 1, 10125 (To), Italy
2 Forschungszentrum Karlsruhe, Institut für Kernphysik, 76021 Karlsruhe, Germany
3 TRIUMF, 4004 Wesbrook Mall, Vancouver, B.C., V6T 2A3 Canada
4 Vienna Environmental Research Accelerator, Faculty of Physics, Universität Wien, Währinger Str. 17, 1090 Wien, Austria
Published online: 21 May 2008
The neutron capture cross section of 209Bi(n,γ)210Bi has been measured using the 3.7 MV Van de Graaff accelerator at Forschungszentrum Karlsruhe. The measurement was carried out by activation of a high purity Bi sample in a quasi-stellar neutron spectrum with kT = 25 keV by employing the 7Li(p,n)7Be reaction at Ep=1912 keV. We performed four activations: two to count the α-activity of 210Po and two more for Accelerator Mass Spectrometry (AMS) analysis at the VERA facility in Vienna. The aim of our study is to measure the partial cross sections to the ground and the isomeric state with improved accuracy, which is necessary to understand the recycling via α-decay of 210, 211Po and the corresponding accumulation of the s-process abundances at the end of the s-path. The Maxwellian averaged cross section for populating the ground state of 210Bi at a thermal energy of kT=30 keV was determined to be <σv>/vT=2.16 ± 0.07 mb. For the isomeric state the measurements are in progress. Based on the present results and on the new data for the stable Pb isotopes measured at n_TOF, we performed a theoretical analysis using stellar models of Asymptotic Giant Branch (AGB) stars. The effect of the new cross section values in the Pb/Bi region was studied by averaging the results of stellar models for M=1.5 and 3 and a half-solar metallicity for the main component, and at [Fe/H]=-1.3 for the strong component. At this lower metallicity the AGB stars have been shown to produce the maximum amount of s-process lead, thus providing a good approximation of the strong component. A study of these aspect is in preparation.
© CEA 2008