Inverse odd-even staggering in nuclear charge radii and possible octupole collectivity in $^{217,218,219}\mathrm{At}$ revealed by in-source laser spectroscopy

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Inverse odd-even staggering in nuclear charge radii and possible octupole collectivity in ${}^{217, 218, 219}{At}$ revealed by in-source laser spectroscopy

A. E. Barzakh et al.

Phys. Rev. C 99, 054317 – Published 14 May 2019

Abstract

Hyperfine-structure parameters and isotope shifts for the 795-nm atomic transitions in ${}^{217, 218, 219}{At}$ have been measured at CERN-ISOLDE, using the in-source resonance-ionization spectroscopy technique. Magnetic dipole and electric quadrupole moments, and changes in the nuclear mean-square charge radii, have been deduced. A large inverse odd-even staggering in radii, which may be associated with the presence of octupole collectivity, has been observed. Namely, the radius of the odd-odd isotope ${}^{218}{At}$ has been found to be larger than the average of its even- $N$ neighbors, ${}^{217, 219}{At}$ . The discrepancy between the additivity-rule prediction and experimental data for the magnetic moment of ${}^{218}{At}$ also supports the possible presence of octupole collectivity in the considered nuclei.

Received 7 March 2019

DOI:https://doi.org/10.1103/PhysRevC.99.054317

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

Published by the American Physical Society

Physics Subject Headings (PhySH)

Charge distributions Fine & hyperfine structure Laser spectroscopy Nuclear structure & decays Spectroscopic factors & electromagnetic moments

A ≥ 220

Nuclear Physics

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Vol. 99, Iss. 5 — May 2019

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Figure 1
Examples of experimental hfs spectra collected for the 795-nm transition. Frequency detuning is shown with respect to the centroid of ${}^{205}{At}$ hfs. The solid red lines represent a fit to the data. The blue lines indicate the calculated positions and relative intensities of the individual hyperfine components. The vertical dashed lines mark the hfs centroids. The isotope, the assumed nuclear spin, the half-life, the α lines used for the photo-ion current monitoring, and the device (windmill [WM] or multireflection time-of-flight mass separator [MR-ToF MS]), see text for details) applied for the measurement are given in each panel. In the case of the WM, the number of recorded α counts of the indicated α line for each frequency step is displayed on the vertical axis. In the case of MR-ToF MS, the number of ions recorded in the MR-ToF MS system for every frequency setting, divided by the total number of counts in a full scan, is given on the vertical axis. In panels (b) and (c) fits of the experimental spectrum of ${}^{218}{At}$ with different possible spin assignments ( $I = 2$ or 3) are shown.
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Figure 2
$g$ factors for the even- $N$ , $N \geq 126$ isotopes of astatine (open circles), francium (squares), actinium (upward triangles), and bismuth (downward triangles). The data points without labels in parentheses correspond to the nuclei with $I^{π} = 9 / 2^{-}$ , whereas the spins for other isotopes are explicitly shown. Lines of the same slope connecting the points for different isotopes are shown.
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Figure 3
Changes in the mean-square charge radii for astatine isotopes near the shell closure at $N = 126$ . Open circles: present work; squares: Ref. [19]. The experimental points are connected by a dotted line to guide the eye. The dashed lines show the droplet model predictions with constant deformation.
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Figure 4
Shell-effect parameters for the lead-region nuclei. Filled squares: parameter $ξ_{even}$ , hollow squares: parameter $ξ_{_{even}}^{*}$ . The experimental points for $ξ_{_{even}}^{*}$ are connected by dotted line to guide the eye. Triangles show the results of the RMF calculations with DD-PC1 energy-density functional.
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Figure 5
Values of the odd-even staggering parameter, γ, for the different isotopic chains in the lead region near the $N = 126$ shell closure: $_{82} Pb$ (squares), $_{84} Po$ (filled upward triangles), $_{85} At$ (hollow circles), $_{86} Rn$ (rightward triangles), $_{87} Fr$ (hollow upward triangles), and $_{88} Ra$ (downward triangles). For ${}^{218}{At}$ the γ values determined with the assumptions $I ({}^{218}{At}) = 2$ and $I ({}^{218}{At}) = 3$ , are both shown. The dotted horizontal line represents the absence of the OES, $γ_{N} = 1$ .
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Physical Review C

covering nuclear physics

Inverse odd-even staggering in nuclear charge radii and possible octupole collectivity in ${}^{217, 218, 219}{At}$ revealed by in-source laser spectroscopy

A. E. Barzakh et al.

Phys. Rev. C 99, 054317 – Published 14 May 2019

Abstract

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Physical Review C

covering nuclear physics

Inverse odd-even staggering in nuclear charge radii and possible octupole collectivity in At217,218,219 revealed by in-source laser spectroscopy

A. E. Barzakh et al.

Phys. Rev. C 99, 054317 – Published 14 May 2019

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Inverse odd-even staggering in nuclear charge radii and possible octupole collectivity in ${}^{217, 218, 219}{At}$ revealed by in-source laser spectroscopy