Recoil isomer tagging in the proton-rich odd-odd N=77 isotones, Tb-142(65)and Ho-144(67) - art. no. 034321

A fusion-evaporation reaction has been employed to search for isomeric stat es in the near-proton drip-line N=77 isotones. Tb-142(65) and Ho-144(67). T he recoiling nuclei were implanted into a silicon detector at the focal pla ne of a gas-filled separator, where a recoil isomer tagging technique was e mployed to correlate prompt and delayed gamma -ray transitions across isome ric states. New states were observed to be built upon a known 15-mus isomer in Tb-142 and the feeding and decay of a new 500(20)-ns isomeric state was established in Ho-144. This measurement represents the first observation o f excited states in Ho-144. The behavior of the new states above the isomer s suggests that they are built upon low-deformation configurations with sig nificant triaxiality. This is in contrast to the lighter-mass proton emitte rs that were recently interpreted as being well-deformed, prolate, axially symmetric nuclei.