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

Abstract

The radioactivity of Os-160(76)84 and W-156(74)82 that lie at the two-proton drip line has been measured in an experiment performed at the Accelerator Laboratory of the University of Jyvaskyla. The Os-160 nuclei were produced using fusion-evaporation reactions induced by a beam of 310 MeV Ni-58 ions bombarding a Cd-106 target. The Os-160 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.. decays of the ground state of Os-160 (E-alpha = 7092(15) keV, t(1/2) = 97(-32)(+97) mu s) and its isomeric state (E-alpha = 8890(10) keV, t(1/2) = 41(-9)(+15) mu s) were measured, allowing the excitation energy of the isomer to be determined as 1844(18) keV. These alpha-decay properties and the excitation energy of the isomer are compared with systematics. The alpha decays were correlated with subsequent decays to investigate the beta decays of the ground state of W-156, 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 Ta-156(73)83 of 333(-22) (+25) ms was obtained in a separate experiment using the same experimental systems with a Pd-102 target. This result was employed to improve the precision of the half-life determined for W-156, which was measured as 157(-34)(+57) ms.