Rotational bands in the proton emitters 131Eu and 141Ho

Proton-decay studies led in recent years to the observation of about 20 new proton emitters. Among others, first two cases of highly deformed proton emitters, namely 131Eu and 141Ho, were reported [1]. Also, the first case of proton-decay fine structure was found in 131Eu [2]. In this work the studies of the deformed proton emitters 131Eu and 141Ho were extended to their excited states using in-beam spectroscopic methods. The experiments were performed at the Argonne National Laboratory using the GAMMASPHERE array of Ge detectors coupled to the Fragment Mass Analyzer. Partial results from this study has been published in [3]. There were no data on excited states in 131Eu and 141Ho prior to this work. Nothing is known on their immediate neighbors. The quadrupole deformation calculated by Moller and Nix for 141Ho is about β2 = 0.29. According to the proton-decay rate calculations [4] half-lives of the two know proton-decaying states in 141Ho are consistent with the 7/2−[523] and 1/2+[411] Nilsson orbitals at this deformation. 131Eu is expected to be even more deformed with β2 = 0.33. Its proton-decay rate and branching ratio to the 2+ state are consistent with the 3/2+[411] orbital.