Measurement of keV-Neutron Capture Cross Sections and Capture Gamma-Ray Spectra of 140Ce and 141Pr

The neutron capture cross sections and capture γ-ray spectra of 140 Ce and 141 Pr were measured in the neutron energy region of 10 to 100 keV and at 550 keV. Prompt γ rays from a capture sample were detected with a large anti-Compton Nal(Tl) spectrometer, employing a neutron time-of-flight method with a 1.5- ns pulsed neutron source by the 7 Li(p, n) 7 Be reaction. A pulse-height weighting technique was applied to observed capture γ-ray pulse-height spectra to extract capture yields. The capture cross sections were derived with the error of about 5% by using the standard capture cross sections of 197 Au. The present results were compared with evaluated values in JENDL-3.2 and previous measurements. The capture γ-ray spectra were obtained by unfolding the observed capture γ-ray pulse-height spectra. An anomalous bump was observed around 1.5 MeV in each γ-ray spectrum of 140 Ce and 141 Pr, and its energy position was consistent with the systematics obtained in our previous work. The multiplicities of the observed capture γ rays were derived from the γ-ray spectra.