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

The radioactivity of ${}_{\phantom{\rule{0.2em}{0ex}}\phantom{\rule{0.2em}{0ex}}\phantom{\rule{0.2em}{0ex}}76}^{160}$Os$_{84}$ and ${}_{\phantom{\rule{0.2em}{0ex}}\phantom{\rule{0.2em}{0ex}}\phantom{\rule{0.2em}{0ex}}74}^{156}$W$_{82}$ 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 $^{160}$Os nuclei were produced using fusion-evaporation reactions induced by a beam of 310 MeV $^{58}$Ni ions bombarding a $^{106}$Cd target. The $^{160}$Os 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 $^{160}$Os (${E}_{\alpha }$ = 7092(15) keV, ${t}_{1/2}$ = 97${}_{-32}^{+97}$ μs) and its isomeric state (${E}_{\alpha }$ = 8890(10) keV, ${t}_{1/2}$ = 41${}_{-9}^{+15}$ μs) were measured, allowing the excitation energy of the isomer to be determined as 1844(18) keV. These α-decay properties and the excitation energy of the isomer are compared with systematics. The α decays were correlated with subsequent decays to investigate the β decays of the ground state of $^{156}$W, revealing that unlike its isotones, both low-lying isomers were populated in its daughter nuclide, $^{156}$Ta. An improved value for the half-life of the proton-decaying high-spin isomeric state in ${}_{\phantom{\rule{0.2em}{0ex}}\phantom{\rule{0.2em}{0ex}}\phantom{\rule{0.2em}{0ex}}73}^{156}$Ta$_{83}$ of 333${}_{-22}^{+25}$ ms was obtained in a separate experiment using the same experimental systems with a $^{102}$Pd target. This result was employed to improve the precision of the half-life determined for $^{156}$W, which was measured as 157${}_{-34}^{+57}$ ms.