Measurement of gamma-rays from the keV-neutron capture by (139)La

The capture cross sections and capture γ-ray spectra of 139 La were measured in a neutron energy region from 10 to 100keV and at 550keV. Pulsed keV neutrons were produced by the 7 Li(p,n) 7 Be reaction with a pulsed proton beam from a Pelletron accelerator. Capture γ-rays were detected with a large anti-Compton NaI(Tl) spectrometer by means of a time-of-flight method. A pulse-height weighting technique was applied to the observed capture γ-ray pulse-height spectra to obtain capture yields. Using the standard capture cross sections of 197 Au, the capture cross sections of 139 La were derived with uncertainties of about 5%. The capture γ-ray spectra were obtained by unfolding the observed capture γ-ray pulse-height spectra. The present results were compared with previous measurements and evaluated values.