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

Abstract

Accepted for publication with Physical Review CThe 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

Collinear laser spectroscopy at ISOLDE: new methods and highlights

“…The r 2 d ⟨ ⟩ and associated trend in odd-even staggering was found to be consistent with a deformed configuration for 218m,219 Fr and 220 Fr marks the border of the region of reflection asymmetry [104]. The g-factor of 219 Fr further supported this interpretation as it closely matched those of 221,223,225 Fr, which are known to be well-deformed nuclei [104]. The 1.5GHz linewidth laser system has proved an ideal method for rapidly locating resonances, which has been recently demonstrated by the measurement of the hyperfine structure and isotope shift of 214 Fr.…”

New charge radius relations for atomic nuclei

“…In recent decades, the enormous progress in size determination of exotic nuclides has been entwined with the realization of radioactive ion beams [3] and fast developments especially in ultra-high-sensitivity laser spectroscopy techniques [4,5]. The new measurements contributed to revealing, for example, the neutron skin effect [6,7] and the nuclear shape variances [8][9][10] when moving far away from the stability line. These new results are among the strongest motivations for the next generations of nuclear physics facilities, in which electron-scattering experiments [11,12] on unstable nu- * Corresponding author: bhsun@buaa.edu.cn † ymzhao@sjtu.edu.cn clei are under way.…”

In-Source Laser Spectroscopy with the Laser Ion Source and Trap: First Direct Study of the Ground-State Properties ofPo217,219

“…An outstanding feature of the δhr 2 i in the region of interest is the odd-even staggering reversal already identified in 86 Rn [64], 87 Fr [37,65], and 88 Ra [66]. This phenomenon has been found to be correlated to the island of octupole deformation [65,66], but the nature of the connection between the two phenomena remains under question [67].…”

“…We present here a performance study of the LIST for nuclei in the region of Z > 82 and N > 126 and its suitability for the study of nuclear ground-state properties. In particular, the list has enabled the first measurement of the hyperfine structure and isotope shift of 217 Po and the first nuclear decay study of 219 Po, which are both of interest to delineate the region of octupoledeformed nuclei [5,37].…”