Abstract
The nuclides 157W and 161Os have been discovered in reactions of 58Ni ion beams with a 106Cd target. The 161Os α-decay energy and half-life were 6890±12 keV and 640±60 μs. The daughter 157W nuclei β-decayed with a half-life of 275±40 ms, populating both low-lying α-decaying states in 157Ta, which is consistent with a 7/2− ground state in 157W. Fine structure observed in the α decay of 161Os places the lowest excited state in 157W with Iπ=9/2− at 318±30 keV. The branching ratio of 5.5−2.2+3.1% indicates that 161Os 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 2f7/2 and 1h9/2 neutron states in N=83 isotones are presented.
Highlights
The nuclides 157W and 161Os have been discovered in reactions of 58Ni ion beams with a 106Cd target
One expects the proton–neutron tensor force component acting between protons filling the 1h11/2 orbital and a single neutron in the 1h9/2 or 2f7/2 orbitals to modify their relative single-particle energies in a specific way that differs from the changes arising only from a central force
Sm were recently measured using transfer reactions [7]. This allowed the centroid energy of the ν1h9/2 orbital relative to the ν2f7/2 orbital to be deduced in these nuclei, see Fig. 1
Summary
The nuclides 157W and 161Os have been discovered in reactions of 58Ni ion beams with a 106Cd target. In this work, focusing on the region at the proton drip line above N = 82, the structure of nuclei is governed at low spin and excitation energy by valence neutrons in the 2f7/2 and 1h9/2 orbitals and protons in the 3s1/2, 2d3/2 and 1h11/2
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