Magnetic moments of thallium isotopes in the vicinity of magic N = 126

The magnetic dipole moments (𝜇) of 209Tl𝑔 (𝑁 = 128) and 207Tl𝑚 (𝑁 = 126) have been measured for the first time using the in-source laser resonance-ionization spectroscopy technique with the Laser Ion Source and Trap (LIST) at ISOLDE (CERN). The application of the LIST suppresses the usually overwhelming background of the isobaric francium isotopes and allows access to heavy thallium isotopes with 𝐴 ⩾ 207. The self-consistent theory of finite Fermi systems based on the energy density functional by Fayans 𝑒𝑡 𝑎𝑙. well describes the 𝑁 dependence of 𝜇 for 1∕2+ thallium ground states, as well as 𝜇 for the 11∕2− isomeric states in europium, gold and thallium isotopes. The inclusion of particle-vibration coupling leads to a better agreement between the theory and experiment for 𝜇(Tl𝑔 , 𝐼 𝜋 = 1∕2+). It is shown that beyond mean-field contributions to 𝜇 cannot be neglected at least for thallium isotopes with 𝐼 𝜋 = 1∕2+.