First proton-pair breaking in semi-magic nuclei beyond 132Sn and 208Pb: Configuration of the long-lived isomer of 217Pa

Abstract

The close similarity between the shell structures in the 132Sn and 208Pb regions is a well known phenomenon. Thus, using the correspondence between the high-j orbits located above the Z=50 and Z=82 shell gaps, we discuss the evolutions of the fully aligned states with one broken proton pair in the N=82 and N=126 isotones. A long-lived isomeric state was discovered in 217Pa more than thirty years ago and despite two other experiments giving new experimental results, the discussions on its main properties (spin, parity, configuration) remained inconclusive. Then, using the comparison with the I^\pi=17/2^+ isomeric state recently measured in 139La, the isomeric state of 217Pa is assigned as the fully aligned state of the (\pi h_{9/2})^2(\pi f_{7/2})^1 configuration.