Skyrme-Hartree-Fock-BCS approach to $^{229m}$Th and neighboring nuclei

Abstract

The microscopic origin of the $^{229m}$Th isomer and its possible manifestation also in neighboring nuclei is explored within a selfconsistent Skyrme Hartree-Fock plus Bardeen-Cooper-Schrieffer approach. By using the well established SIII Skyrme parametrization, without any special adjustments related to low-energy isomer, the single-particle spectrum provided by the model reproduces the correct isomer $K^{\pi}=3/2^{+}$ spin and parity, and the relative proximity of the isomeric state to the $K^{\pi}=5/2^{+}$ ground state, yet on the keV scale. We show that this approach may provide microscopic estimates for some related observables, such as the quadrupole and octupole moments, deformation parameters as well as magnetic dipole moments. Its ability to provide a prediction for the M1 isomer transition probability is discussed. The obtained $^{229}$Th single-particle structure is compared with that provided by calculations in neighbouring actinide isotopes and isotones, allowing us to assess the more general role of the considered mechanism for the formation of low-energy isomers.