Recent theoretical developments applying collective and microscopic nuclear-structure models to study the ^229mTh clock isomer will be presented. A common starting point of the approaches employed is the circumstance that being a member of the light actinive mass region the nucleus ²²⁹Th exhibits pronounced reflection-asymmetric (octupole) shape properties which together with the underlying intrinsic structure determine the specific conditions for the isomer formation. It will be shown that a collective quadrupole-octupole core plus paricle model approach allows one to understand the formation of the isomer as the result of a very fine interplay between collective axial quadrupole-octupole (pear-shape) modes and single-particle motion which determines the energy and electromagnetic properties of the isomer [1,2,3]. Within a microscopic self-consistent Hartree-Fock plus BCS (HFBCS) approach with Skyrme effective interaction it will be shown that together with the pear-shape deformation the pairing interaction also plays a crucial role in the ^229mTh formation. It will be shown that by determining the pairing strength with respect to the moment of inertia characteristics of the nucleus one obtains the isomer energy in the range of few tens of keV [4]. Further decrease of the energy can be achieved through finer variation of the pairing constants. The latter brings the calculated ^229mTh energy into a sub keV range allowing for a consistent theoretical assessment of the isomer transition sensitivity to possible temporal variations of fundamental constants.

References

[1] N. Minkov and A. Pálffy, “Reduced Transition Probabilities for the Gamma-decay of the 7.8 eV Isomer in ²²⁹Th”, Phys. Rev. Lett. 118, 212501 (2017).

[2] N. Minkov and A. Pálffy, “Theoretical Predictions for the Magnetic Dipole Moment of ^229mTh”, Phys. Rev. Lett. 122, 162502 (2019).

[3] N. Minkov and A. Pálffy, “^229mTh isomer from a nuclear model perspective”, Phys. Rev. C 103, 014313 (2021).

[4] N. Minkov, A. Pálffy, P. Quentin and L. Bonneau, “Skyrme-Hartree-Fock-BCS approach to ^229mTh and neighboring nuclei”, Phys. Rev. C 110, 034327 (2024).  

Biography

Prof. Nikolay Minkov is a Full Professor of Theoretical Nuclear Physics at the Institute for Nuclear Research and Nuclear Energy (INRNE), Bulgarian Academy of Sciences. He earned his Master of Science degree from Sofia University and subsequently obtained two doctoral degrees from INRNE, BAS: one in Physics (focused on algebraic theories in nuclear structure) and a higher DSc degree in complex deformed nuclear models. His academic career is dedicated to pioneering research in theoretical nuclear physics.

Inviter: Xiao Lu