Speaker
Description
The Isotope Separator On Line DEvice (ISOLDE) is a facility for the production and study of radioactive ion beams at CERN. The Laser Ion Source and Trap (LIST) of the Resonance Ionization Laser Ion Source (RILIS) enables access to isotopes that otherwise suffer from strong isobaric contamination [1,2].
We report the continued study of neutron-rich polonium ($Z=84$) isotopes through in-source laser spectroscopy with LIST, where improved suppression of isobaric francium contamination enabled extension of measurements up to $^\text{220}\text{Po}$. Alpha-decay spectra were recorded with the ISOLDE Decay Station (IDS) with sufficient resolution to distinguish between polonium ground and isomeric states as well as isobaric contaminants.
From isotope shifts and hyperfine structure in atomic transitions, the changes in mean-squared charge radii $\langle r^2 \rangle$ and the magnetic dipole and electric quadrupole moments of $^{219,220}\text{Po}$ ground states and the high-spin isomers $^{\text{211m,212m}}\text{Po}$ were extracted for the first time. For $^\text{204,206-211,217,218}\text{Po}$, the obtained values agree with literature [2-6]. Comparison to single-particle and empirical moments calculated with the additivity relation suggests a marked difference in $\nu1i_{11/2}$ occupation between the isomeric and ground states of $^{211,212}\text{Po}$. According to several DFT calculations [7,8], occupation of this orbital determines the kink in the $\langle r^2 \rangle$ at $N=126$.
The LIST furthermore enabled the first detailed spectroscopy of $^{219,220}\text{Po}$ with IDS and the Alpha SETup (ASET), and a summary will be presented.
[1] D. Fink et al., Nucl. Instrum. Methods Phys. Res. B 344, 83 (2015)
[2] D. A. Fink et al., Phys. Rev. X 5, 011 018 (2015)
[3] D. Kowalewska et al., Nucl. Shapes Struct. Low Excit. Energies, 93 (1992)
[4] M. Seliverstov et al., Phys. Lett. B 719, 362 (2013)
[5] T. E. Cocolios et al., Phys. Rev. Lett. 106, 052 503 (2011)
[6] M. Seliverstov et al., Phys. Rev. C 89, 034 323 (2014)
[7] P. M. Goddard et al., Phys. Rev. Lett. 110, 032 503 (2013)
[8] U. C. Perera and A. V. Afanasjev, Phys. Rev. C 107, 064 321 (2023)