The neutron capture cross section of ${}^{139}\mathrm{La}$ has been measured relative to that of ${}^{197}\mathrm{Au}$ by means of the activation method. The sample was irradiated in a quasistellar neutron spectrum for $kT=25\mathrm{}\mathrm{keV}$ generated via the ${}^7\mathrm{Li}{\mathrm{}(p,n)\mathrm{}}^7\mathrm{Be}$ reaction with the proton energy adjusted 30 keV above the threshold. Maxwellian averaged neutron capture cross sections were calculated for energies $kT=5\mathrm{}–100\mathrm{keV}.$ The new value for $kT=30\mathrm{}\mathrm{keV}$ is found to be $31.6\pm 0.8\mathrm{mb},$ 18% lower and considerably less uncertain than the previously recommended value of $38.4\pm 2.7\mathrm{mb}.$ With these results the s- and r-process components could be more accurately determined, making lanthanum a reliable s- and r-process indicator in stellar spectroscopy.

• Received 13 June 2003

DOI:https://doi.org/10.1103/PhysRevC.68.035801