Recoil isomer tagging in the proton-rich odd-odd N = 77 isotones, 142Tb and 144Ho

Abstract

A fusion-evaporation reaction has been employed to search for isomeric states in the near-proton drip-line N577 isotones, 65 142Tb and 67 144Ho. The recoiling nuclei were implanted into a silicon detector at the focal plane of a gas-filled separator, where a recoil isomer tagging technique was employed to correlate prompt and delayed g-ray transitions across isomeric states. New states were observed to be built upon a known 15-ms isomer in 142Tb and the feeding and decay of a new 500(20)-ns isomeric state was established in 144Ho. This measurement represents the first observation of excited states in 144Ho. The behavior of the new states above the isomers suggests that they are built upon low-deformation configurations with significant triaxiality. This is in contrast to the lighter-mass proton emitters that were recently interpreted as being well-deformed, prolate, axially symmetric nuclei.