In-beam study of high-spin few-particle states and the decay of an isomer in 151Tb

Abstract

Abstract Levels in 151Tb have been populated in (α, 4n) and (τ, 3n) reactions on an 151Eu target and the decay of these levels has been studied in-beam. Excitation functions, angular distributions and γγ coincidences are measured using Ge(Li) spectrometers. Also, conversion electrons and delayed γ-rays have been recorded. The measurements have revealed a 25 s isomeric 11 2 − level decaying via levels with spin and parity 5 2 + and 3 2 + to the 1 2 + ground state. The isomer and a 15 2 + state are fed through two similar level sequences, which have been established up to levels with spin and parity Equal to 31 2 − ( 35 2 − and 35 2 + ( 39 2 + ) , respectively. Another level sequence ranges from 33 2 (+) to ( 45 2 + ) . The levels with spin below 11 2 are interpreted as shell-model excitations of the odd proton. The high-spin states are ascribed to excitations of the five valence nucleons outside the magic 64146Gd82 core. In particular, a reasonable interpretation of the high-spin level sequences is obtained if the three-particle clusters (π h 11 2 vf 7 2 vh 9 2 ) 27 2 ) − and (π h 11 2 vh 9 2 vi 13 2 ) 33 2 + are assumed topersist as stable components within the sequences. The stability of these clusters is explained as a result of the maximization of the overlap of nucleonic wave functions that is obtained by alignment of angular momentum (MONA).