Gamma rays from inelastic scattering of 2.9-MeV neutrons by 55Mn, 59Co, 63Cu, 65Cu, 139La, and 141Pr

Abstract

Gamma rays produced by inelastic scattering of 2.9-MeV neutrons on 55Mn, 59Co, 63Cu, 65Cu, 139La, and 141Pr were observed, using a lithium-drifted germanium detector. Coincidences between these gamma rays were observed, using a sodium iodide detector and a lithium-drifted germanium detector. It was possible to resolve gamma rays, hitherto unresolved, to determine their energies to within ±1 keV in most cases, and to determine their relative intensities to within ±30%.From the energies of the gamma rays and the knowledge of which gamma rays are in coincidence, level diagrams were constructed for these nuclei. There was no reason to dispute the presently accepted level scheme for 55Mn, 59Co, 63Cu, and 65Cu, but the energies of the known levels were determined with greater precision. Two new levels, at 1685 and 1715 keV, are proposed for 139La, and four new levels, at 1117, 1350, 1437, and 1451 keV, are proposed for 141Pr. The decay of 141Nd to 141Pr was examined, and the previously published decay scheme was confirmed. In addition, another weak K-capture branch, to a level at 1437 keV, was found. No evidence is seen for the previously suggested levels at 880 keV in 141Pr and at 800 keV in 139La.The relative production rates of the excited states of all these nuclei were fitted to the Hauser–Feshbach model of inelastic neutron scattering. The earlier determinations of the spins of the first four excited states of 55Mn are confirmed and a spin of 9/2 is suggested for the level at 1883 keV. Spins are suggested for all the levels of 59Co, up to and including the level at 1745 keV. These differ from all the three previously published spin determinations. The spin assignments previously published for the first three excited states of 63Cu and 65Cu are confirmed and spins are suggested for the next three excited states. For both 139La and 141Pr, only the spins of the ground state and the first excited state were known; in each case spins are suggested for the next six excited states.