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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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Cho, Y. et al, & Perez-Vidal, R. M. (2026). Regularity of core coupled high-spin structure in neutron-rich 196-202Au isotopes approaching N=126. Phys. Lett. B, 878, 140558–7pp.
Abstract: Excited states built upon long-lived high-spin isomers in hard-to-reach neutron-rich Au (Z = 79) isotopes were populated using multi-nucleon transfer reactions between 136Xe and 198Pt at 7 MeV/u. These states in 196,198-202Au were identified for the first time using the powerful combination of the VAMOS++ spectrometer, the CATLIFE detection system, and the AGATA 1-ray tracking array. Their measured energies exhibit remarkable regularity as a function of neutron number and are seen to be inherited from the energies of yrast-band members in the corresponding Hg (Z = 80) isotope. Large-scale shell-model calculations reproduce the observed regularity and show that these states arise from the unique-parity orbitals 20h11/2 and v0i13/2 coupled to the Hg core. This regularity is due to the dominant proton configurations of the Hg and Au isotopes, where the level energies are almost independent of different neutron-orbital occupancies. The calculated Au wave functions show significant higher-spin components of the corresponding Hg core, unlike what is expected in the conventional interpretation in terms of the weak-coupling/decoupling limits of the particle-core coupling model.
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