Discovery of W-157 and Os-161

WOS: 000278933900003
The nuclides W-157 and Os-161 have been discovered ill reactions of Ni-58 ion beams with a Cd-106 target. The Os-161 alpha-decay energy and half-life were 6890 +/- 12 keV and 640 +/- 60 mu s. The daughter W-157 nuclei beta-decayed with a half-life of 275 +/- 40 ms, populating both low-lying alpha-decaying states in Ta-157, which is consistent with a 7/2(-) ground state in W-157. Fine structure observed in the alpha decay of Os-161 places the lowest excited state in W-157 with 1(pi) = 9/2(-) at 318 +/- 30 key. The branching ratio of 5.5(-2.2)(+3.1)% indicates that Os-161 also has a 7/2(-) ground state. Shell-model calculations analysing the effects of monopole shifts and a tensor force on the relative energies of 2f(7/2) and 1h(9/2) neutron states in N = 83 isotones are presented. (C) 2010 Elsevier B.V. All rights reserved.
Jyvaskyla; United Kingdom Science and Technology Facilities Council; Swedish Natural Science Research Council; Academy of Finland [44875, 209430, 111965]; European Union [R113-CT-2004-506065, HPMT-CT-2001-00250]; Science and Technology Facilities Council [EP/C015266/1, EP/C015371/1, ST/G008671/1, ST/F012012/1, ST/J000108/1, EP/C543157/1, ST/G008620/1, ST/F012039/1]
We thank the accelerator staff at Jyvaskyla for their excellent support and Paul Morrall from Daresbury Laboratory for making the targets. This work was supported by the United Kingdom Science and Technology Facilities Council; the Swedish Natural Science Research Council; the Academy of Finland through the Finnish Centre of Excellence Programme (project 44875 Nuclear and Condensed Matter Physics Programme at JYFL) and support for C.S. (contract 209430) and P.T.G. (contract 111965); the European Union Sixth Framework contract EURONS (R113-CT-2004-506065) and the European Union Marie Curie Programme (contract HPMT-CT-2001-00250).