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Laser spectroscopy of francium isotopes at the borders of the region of reflection asymmetry

Abstract : 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 $\delta\langle r^{2}\rangle^{A,221}$ 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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http://hal.in2p3.fr/in2p3-01065500
Contributor : Sophie Heurteau <>
Submitted on : Thursday, September 18, 2014 - 10:56:37 AM
Last modification on : Wednesday, September 16, 2020 - 4:08:37 PM

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I. Budinčević, J. Billowes, M. L. Bissell, T. E. Cocolios, R. P. de Groote, et al.. Laser spectroscopy of francium isotopes at the borders of the region of reflection asymmetry. Physical Review C, American Physical Society, 2014, 90, pp.014317. ⟨10.1103/PhysRevC.90.014317⟩. ⟨in2p3-01065500⟩

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