Blurring the Boundaries: Decays of Multiparticle Isomers at the Proton Drip Line

Abstract

A multiparticle spin-trap isomer has been discovered in the proton-unbound nucleus 158 73Ta85. The isomer mainly decays by γ-ray emission with a half-life of 6.1ð1Þ μs. Analysis of the γ-ray data shows that the isomer lies 2668 keV above the known 9þ state and has a spin 10ℏ higher and negative parity. This 19− isomer also has an 8644(11) keV, 1.4(2)% α-decay branch that populates the 9þ state in 154Lu. No proton-decay branch from the isomer was identified, despite the isomer being unbound to proton emission by 3261(14) keV. This remarkable stability against proton emission is compared with theoretical predictions, and the implications for the extent of observable nuclides are considered.