The neutron capture cross section of 139La has been measured at a thermal energy of kT = 5 keV by means of the activation technique. Three irradiations were performed in a quasi-stellar neutron spectrum at the Karlsruhe 3.7 MV pulsed Van de Graaff accelerator, and the induced activities were measured by means of HPGe clover detectors. The final cross section of 113.7 ± 4.0 mbarn was found to be 10% higher than that previously assumed. Together with an earlier measurement at kT = 25 keV, Maxwellian-averaged neutron capture cross sections at the relevant thermal energies of the main s-process component, i.e., at kT = 8 and 23 keV, could be reliably interpolated. The s-abundances obtained on the basis of these data showed that the r-process contribution to solar lanthanum, Nr = N☉ - Ns, is 30%. This is in good agreement with the lanthanum abundance of extremely metal-poor and very r-process-rich stars.
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