Measurement of capture gamma rays from the broad 53-keV and the narrow 35-keV neutron resonances of Na-23

The capture gamma rays from the broad 53-keV and the narrow 35-keV p-wave n eutron resonances of Na-23 were measured using a large anti-Compton HPGe ga mma -ray spectrometer. A neutron time-of-flight method was adopted with a 1 .5-ns wide pulsed-neutron source by the Li-7(p, n)Be-7 reaction. The standa rd capture cross sections of Au-197 and pulse-height weighting technique we re employed to determine the number of neutrons incident on a capture sampl e. The numbers of observed primary gamma -ray transitions were 15 and 13 fo r the 53- and 35-keV resonances, respectively. The partial capture kernels and the partial radiative widths corresponding to these transitions were de rived for the first time. The total radiative widths of these resonances we re also derived. The present results are compared with measurements by othe r authors and evaluations. Moreover, a new 4,909-keV state in Na-24 was fou nd and its spin and branching ratio were determined from the analysis of th e gamma -ray transitions from the narrow 35-keV resonance.