Radiative neutron capture in La-139 below 2.5 keV

The radiative neutron capture cross section of 139La has been measured in the energy region of 70 -- 2,540 eV using the 52 m neutron time-of-flight facility at the Japan Atomic Energy Research Institute electron linac. Neutron capture events were detected with a 3,500 l liquid scintillator tank. Individual resonances were analyzed using the area analysis method to obtain the capture widths. Capture data were corrected for the multiple scattering of neutrons in a sample by means of the Monte Carlo technique. Capture areas gGAMMA sub(n)GAMMA sub(γ)/GAMMA for 20 resonances and capture widths GAMMA sub(γ) for 5 resonances were newly obtained. The present average capture cross section above 1.6 keV can be well reproduced by the statistical model calculation with the available average resonance parameters, but below 1.6 keV is found to deviate from its prediction. (author)