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Andreyev, A. N. et al, Algora, A., & Nacher, E. (2025). Electromagnetic moments of 215,217Bi: Probing shell evolution beyond N=126. Phys. Lett. B, 871, 140013–9pp.
Abstract: The nuclear properties of bismuth isotopes (Z = 83), with just one valence proton above the closed spherical shell at Z = 82, are expected to be governed by a single unpaired proton. However, already in semimagic 209Bi (Z = 83, N = 126), the magnetic moment (mu) strongly deviates from the single-particle Schmidt value. A near linear decrease in μwith the increase of N after the N = 126 magic number was observed up to N = 130. In order to test whether this trend is kept at N> 130 and to reveal the underlying mechanisms, an investigation of Bi-215,Bi-217 (N = 132, 134) has been undertaken. The magnetic dipole and electric quadrupole moments of the I-x= 9/2-nuclear ground states in these isotopes have been measured for the first time using the in-source resonance-ionization spectroscopy technique at ISOLDE (CERN). It has been shown that the linearly decreasing trend of mu(Bi-209,211,213(g)) is broken in Bi-215,Bi-217 with a nearly constant value of μobserved. Experimental data have been compared to calculations in the framework of the configuration-interaction shell model with the monopole-based universal VMU+LS interaction. The peculiarities in the behavior of μ(Bi, 9/2-) with increasing neutron number are explained as being due to the shell evolution, change of the neutron orbitals occupancies and strong configuration mixing beyond N = 130. Also, the difference in the μtrends for bismuth (Z = 83) and astatine (Z = 85) isotopes with N> 126 are reproduced by the shell-model calculations. It is shown that monopole interaction plays noticeable role in the description of the peculiarities of the μbehaviour. Additionally, the extension of the application of the V-MU interaction to the μisotopic trends for heavy nuclei is important for further study of the capabilities of this promising version of the shell-model calculations.
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Yue, Z. et al, Algora, A., & Nacher, E. (2024). Magnetic moments of thallium isotopes in the vicinity of magic N=126. Phys. Lett. B, 849, 138452–7pp.
Abstract: The magnetic dipole moments (mu) of Tl-209(g)(N =128) and Tl-207(m)(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 >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 μfor 1/2(+) thallium ground states, as well as μfor 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 mu(Tl-g , I-pi = 1/2(+)). It is shown that beyond mean-field contributions tocannot be neglected at least for thallium isotopes with I-pi = 1/2(+).
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