In-Source Laser Spectroscopy with the Laser Ion Source and Trap: First Direct Study of the Ground-State Properties of $^{217;219}$Po
Résumé
A Laser Ion Source and Trap (LIST) for a thick-target, isotope-separation on-line facility has been
implemented at CERN ISOLDE for the production of pure, laser-ionized, radioactive ion beams. It offers
two modes of operation, either as an ion guide, which performs similarly to the standard ISOLDE
resonance ionization laser ion source (RILIS), or as a more selective ion source, where surface-ionized ions
from the hot ion-source cavity are repelled by an electrode, while laser ionization is done within a radiofrequency
quadrupole ion guide. The first physics application of the LIST enables the suppression of
francium contamination in ion beams of neutron-rich polonium isotopes at ISOLDE by more than 1000
with a reduction in laser-ionization efficiency of only 20. Resonance ionization spectroscopy is performed
directly inside the LIST device, allowing the study of the hyperfine structure and isotope shift of 217Po for
the first time. Nuclear decay spectroscopy of 219Po is performed for the first time, revealing its half-life, α-
to-β-decay branching ratio, and α-particle energy. This experiment demonstrates the applicability of the
LIST at radioactive ion-beam facilities for the production and study of pure beams of exotic isotopes.