LEVELS IN Tb$sup 159$ POPULATED IN THE DECAY OF Gd$sup 15$$sup 9$

The beta decay of 18-hr Gd/sup 159/ was investigated with magnetic beta- ray spectrometers and by scintillation spectroscopy. The Gd/sup 159/ source was produced by neutron irradiation of gadolinlum enriched in the isotope Gd/sup 158/ to 97.6%. The internal conversion and gamma ray scintillation measurements were performed with a source produced by isotope separation after the activation. The gamma ray spectrum was also studied by the external conversion method. Gamma rays having the energies 348.0 plus or minus 0.4, 536 plus or minus 2, 557 plus or minus 2, 580 plus or minus 1, and 616 plus or minus 2 kev were observed in this decay. The relative intensities of these gamma rays were obtained from the photoelectron lines after correction for the angular dependence of the photoelectric process. In addition to the levels at 58.0, 137.5, and 363.2 kev previously known to be populated in the decay of Gd/sup 159/, levels in Tb/sup 159/ at 348.0, 580, 616, and 674 kev are suggested to be fed in this beta decay. M1 character is suggested for the 348-kev gamma ray from measured K conversion coefficient. The upper limit found for the K conversion coefficient of the 305-kev transition indicates E1more » multipolarity. The log ft value obtained for the beta ray to the 348-kev level indicates a hindered, first forbidden transition in agreement with the 3/2/sup -/ STA521! assignment for the ground state of Gd/sup 159/ and the 5/2/sup +/ STA413! classification of the 348-kev level. The log ft values found for the beta decay to the 580-, 616-, and 674-kev levels are in agreement with the 1/2/sup +/, 3/2/sup +/, and 5/2/sup +/ assignments previously suggested from recently performed Coulomb excitation experiments on Tb/sup 159/. The possibility of gamma -vibrational character of these levels is discussed. (auth)« less