Measurements of keV-Neutron Capture Cross Sections and Capture Gamma-Ray Spectra of 77Se

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The neutron capture cross sections and capture γ-ray spectra of 77Se were measured in a region from 15 to 100 keV and at around 510 keV. A neutron time-of-flight method was used with a ns-pulsed neutron source based on the 7Li(p,n)7Be reaction and with a large anti-Compton NaI(Tl) γ-ray spectrometer. A pulse-height weighting technique was applied to the observed γ-ray pulse-height spectra to obtain capture yields. The capture cross sections were derived with errors less than 5%, by using the standard capture cross sections of 197Au. The present results were the first experimental ones above the resolved resonance region, and compared with the evaluated values in JENDL-3.3, ENDF/B-VI.8, and ENDF/B-VII.0. The evaluated values in those libraries were smaller than the present results by 10–20% in the region from 15 to 100 keV. At around 510 keV, the values in JENDL-3.3 and ENDF/B-VII.0 were smaller than the present result by about 20%, but those in ENDF-VI.8 were larger than the present result by about 20%. The capture γ-ray spectra of 77Se were derived by unfolding the observed capture γ-ray pulse-height spectra. The present results were the first experimental ones in the keV region.