High-spin states in 154Er and parallel proton- and neutron-core breaking

Abstract High-spin states of 154 Er have been studied using the 21 Compton-suppressed detector array HERA following the 118 Sn( 40 Ar, 4n) reaction at 180 MeV. A detailed analysis of the triple coincidences was performed and the level scheme of 154 Er could be built up to spin 42ℏ. Calculations were performed using the deformed Woods-Saxon cranking approximation, taking into account the pairing forces. The decay scheme evolves from a weakly collective rotational structure at the lower spins to a typical non-collective one including a few characteristic multiplet-sequences: (f 7 2 2 ) 6,4,2,0 and (h 11 2 4 ) 16,14,12,10 . The most striking feature seems to be the existence, above the I π = 36 + state (which has the maximum angular momentum available from alignment of the valence particles), of two parallel unconnected decay paths involving the separate breaking of the neutron and proton cores.