K isomers in 254No:: Probing single-particle energies and pairing strengths in the heaviest nuclei

We have identified two isomers in No-254, built on two- and four-quasiparticle excitations, with quantum numbers K-pi=8(-) and (14(+)), as well as a low-energy 2-quasiparticle K-pi=3(+) state. The occurrence of isomers establishes that K is a good quantum number and therefore that the nucleus has an axial prolate shape. The 2-quasiparticle states probe the energies of the proton levels that govern the stability of superheavy nuclei, test 2-quasiparticle energies from theory, and thereby check their predictions of magic gaps.