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

Abstract

The radioactivity of 160 76Os84 and 156 74W82 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 (𝐸𝛼 = 7092(15) keV, 𝑡1∕2 = 97+97 −32 μs) and its isomeric state (𝐸𝛼 = 8890(10) keV, 𝑡1∕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 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 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 156 73Ta83 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.