In-Source Laser Spectroscopy with the Laser Ion Source and Trap: First Direct Studyof the Ground-State Properties of $^{217;219}$Po

International audienceA Laser Ion Source and Trap (LIST) for a thick-target, isotope-separation on-line facility has beenimplemented at CERN ISOLDE for the production of pure, laser-ionized, radioactive ion beams. It offerstwo modes of operation, either as an ion guide, which performs similarly to the standard ISOLDEresonance ionization laser ion source (RILIS), or as a more selective ion source, where surface-ionized ionsfrom the hot ion-source cavity are repelled by an electrode, while laser ionization is done within a radiofrequencyquadrupole ion guide. The first physics application of the LIST enables the suppression offrancium contamination in ion beams of neutron-rich polonium isotopes at ISOLDE by more than 1000with a reduction in laser-ionization efficiency of only 20. Resonance ionization spectroscopy is performeddirectly inside the LIST device, allowing the study of the hyperfine structure and isotope shift of 217Po forthe 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 theLIST at radioactive ion-beam facilities for the production and study of pure beams of exotic isotopes