Hindered decays from a non-yrast four-quasiparticle isomer in 164Er

The half-life of a Kπ=12⁺ isomer in 164Er has been measured to be 68(2) ns, and new decay pathways have been identified. These include highly K-forbidden γ-ray transitions directly to the ground-state rotational band, with reduced hindrance values that can be compared with those found for heavier nuclides. The new data support the interpretation that the level density is a key variable in determining K-forbidden transition rates.