Abstract
The spectroscopic electric quadrupole moment of the neutron-deficient francium isotope 203 Fr was measured by using high-resolution collinear resonance ionization spectroscopy (CRIS) at the CERN Isotope Separation On-Line Device (ISOLDE) facility. A remeasurement of the 207 Fr quadrupole moment was also performed, resulting in a departure from the established literature value. A sudden increase in magnitude of the 203 Fr quadrupole moment, with respect to the general trend in the region, points to an onset of static deformation at N = 116 in the 87 Fr isotopic chain. Calculation of the static and total deformation parameters show that the increase in static deformation only cannot account for the observed departure of its relative charge radius from the 82 Pb chain.
Highlights
Neutron-deficient isotopes in the vicinity of the Z = 82 and N = 126 shell closures have been the subject of continued experimental and theoretical interest
For odd-Z, even-N nuclei above Z = 82 and below N = 126, a competition arises between the spherical π 1h9/2 ground state and oblate π 3s1/2 intruder state
We present the first high-resolution laser spectroscopy study of 203Fr
Summary
Low-lying states with shape configurations that differ from the ground state lead to shape coexistence in the region [1]. For odd-Z, even-N nuclei above Z = 82 and below N = 126, a competition arises between the spherical π 1h9/2 ground state and oblate π 3s1/2 intruder state. The excitation energy of this intruder state decreases as the neutron orbitals below N = 126 are depleted. This state inverts with the π 1h9/2 state to become the ground state in 18835Bi [2] and 18955At [3]. In 87Fr, it is predicted to become the ground state in 199Fr [4,5,6,7]
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