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تسجيل مستخدم جديدLaser spectroscopy of francium isotopes at the borders of the region of reflection asymmetry
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The magnetic dipole moments and changes in mean-square charge radii of the neutron-rich $^{218m,219,229,231}text{Fr}$ isotopes were measured with the newly-installed Collinear Resonance Ionization Spectroscopy (CRIS) beam line at ISOLDE, CERN, probing the $7s~^{2}S_{1/2}$ to $8p~^{2}P_{3/2}$ atomic transition. The $deltalangle r^{2}rangle^{A,221}$ values for $^{218m,219}text{Fr}$ and $^{229,231}text{Fr}$ follow the observed increasing slope of the charge radii beyond $N~=~126$. The charge radii odd-even staggering in this neutron-rich region is discussed, showing that $^{220}text{Fr}$ has a weakly inverted odd-even staggering while $^{228}text{Fr}$ has normal staggering. This suggests that both isotopes reside at the borders of a region of inverted staggering, which has been associated with reflection-asymmetric shapes. The $g(^{219}text{Fr}) = +0.69(1)$ value supports a $pi 1h_{9/2}$ shell model configuration for the ground state. The $g(^{229,231}text{Fr})$ values support the tentative $I^{pi}(^{229,231}text{Fr}) = (1/2^{+})$ spin, and point to a $pi s_{1/2}^{-1}$ intruder ground state configuration.
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