Decay spectroscopy at the two-proton drip line: radioactivity of the new nuclides ¹⁶⁰Os and ¹⁵⁶W

The radioactivity of ¹⁶⁰₇₆Os₈₄ and ¹⁵⁶₇₄W₈₂ that lie at the two-proton drip line has been measured in an experiment performed at the Accelerator Laboratory of the University of Jyväskylä. The ¹⁶⁰Os nuclei were produced using fusion-evaporation reactions induced by a beam of 310 MeV ⁵⁸Ni ions bombarding a ¹⁰⁶Cd target. The ¹⁶⁰Os ions were separated in flight using the recoil separator MARA and implanted into a double-sided silicon strip detector, which was used to measure their decays. The α decays of the ground state of ¹⁶⁰Os (E_α = 7092(15) keV, t_1/2 = 97⁺⁹⁷_-32 μs) and its isomeric state (E_α = 8890(10) keV, t_1/2 = 41⁺¹⁵_-9 μs) were measured, allowing the excitation energy of the isomer to be determined as 1844(18) keV. These α-decay properties were correlated with subsequent decays to investigate the β decays of the ground state of ¹⁵⁶W, revealing that unlike its isotones, both low-lying isomers were populated in its daughter nuclide, ¹⁵⁶Ta. An improved value for the half-life of the proton-decaying high-spin isomeric state in ¹⁵⁶₇₃Ta₈₃ of 333⁺²⁵_-22 ms was obtained in a separate experiment using the same experimental systems with a ¹⁰²Pd target. This result was employed to improve the precision of the half-life determined for ¹⁵⁶W, which was measured as 157⁺⁵⁷_-34 ms.