Measurement of keV-Neutron Capture Cross Sections and Capture Gamma-Ray Spectra of²⁰⁹Bi

Abstract

The capture cross sections and capture -ray spectra of 209 Bi were measured in a neutron energy region from 5 to 80 keV and at 520 keV, using pulsed keV neutrons from the 7 Li(p; n) 7 Be reaction and a time-of-flight method. The capture rays from a bismuth or standard gold sample were detected with a large anti-Compton NaI(Tl) spectrometer. The capture yield of the bismuth or gold sample was obtained by applying a pulse-height weighting technique to the corresponding capture -ray pulse-height spectrum. The derived capture cross sections from 5 to 80 keV were in good agreement with recent measurements, but that at 520 keV was about half of previous measurements. This large discrepancy at 520 keV was ascribed to the incorrect background-subtraction in the previous measurements from a comparison between the present and previous capture -ray spectra. Strong transitions from the capture states to low lying states of 210 Bi were observed in the present -ray spectra. The multiplicities of observed rays were obtained from the -ray spectra.