Puzzle on isomeric configurations in and around N=126 closed shell

Abstract

The puzzle of finding consistent nuclear configurations to explain both the decay probabilities and moments of the 9/2-, 8+, and 21/2- isomers in and around the N=126 closed shell has been approached in the generalized seniority scheme. Though h9/2 is the dominant orbital near Fermi energy, the role of configuration mixing from the surrounding f7/2 and i13/2 orbitals is found to be very important for the consistent explanation of all the isomeric properties such as the B(E2) rates, Qmoments, and gfactors. The structural behavior of the closed shell N=126 isotonic isomers turns out to be very similar to that of the N=124 and N=128 isotonic isomers, which have two neutron holes and two neutron particles, respectively. This is due to the pairing symmetries of nuclear many-body Hamiltonian. As confirmation, the microscopic shell model occupancies are also calculated for these isomers in the N=126 chain which support the generalized seniority results. Additional arguments using the systematics of odd-proton 9/2- states in Tl (Z=81), Bi (Z=83), At (Z=85), and Fr (Z=87) isotopes are also presented.