Abstract
Hyperfine-structure parameters and isotope shift of the 9/2$^−$ isomeric state in $^{187}$Au relative to $^{197}$Au for the 267.6-nm atomic transition have been measured for the first time using the in-source resonance-ionization spectroscopy technique. The magnetic dipole moment and change in the mean-square charge radius for this 9/2$^−$ isomer have been deduced. The observed large isomer shift relative to the 1/2$^+$ ground state in $^{187}$Au confirms the occurrence of the shape coexistence in $^{187}$Au proposed earlier from the analysis of the nuclear spectroscopic data and particle plus triaxial rotor calculations. The analysis of the magnetic moment supports the previously proposed 9/2$^−$, 1/2$^−$[541] assignment at moderate prolate deformation for $^{187}$Au$^m$.
Highlights
The neutron-deficient isotopes near Z = 82 exhibit one of the most extensive manifestations of shape coexistence known anywhere on the nuclear chart [1]
The jumps in the mean-square charge radius extracted from the isotope shift (IS) values are directly related to differences in nuclear deformation as demonstrated by the exemplary shape staggering in the mercury nuclei (Z = 80) at N = 100–105 [3,4,5]
Where ν0 is the centroid frequency of the hfs, the prime symbol denotes the upper level of the atomic transition, C = F (F + 1) − I (I + 1) − J (J + 1), F is the total angular momentum of the atomic level, I and J are the nuclear spin and the angular momentum for the electronic state, respectively, and anl is the magnetic hyperfine coupling constant for the atomic level with the quantum numbers n and l
Summary
The neutron-deficient isotopes near Z = 82 exhibit one of the most extensive manifestations of shape coexistence known anywhere on the nuclear chart [1]. The neighboring neutron-deficient gold isotopes (Z = 79) provide another example of an abrupt change in the groundstate mean-square charge radius (at N = 107). This jump is due to the transition from weakly oblate (A > 186) to strongly prolate-deformed (A = 183–186) shapes [6,7,8,9]. The isotope 187Au108 lies in the immediate vicinity of this jump and exhibits multiple-coexisting structures [10,11].
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