Abstract
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, ?- to-?-decay branching ratio, and ?-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.
Highlights
The study of radioactive neutron-rich nuclei in the lead region, where Z 1⁄4 82 is a nuclear magic number, is an experimental challenge
Heavier nuclei is distributed over a wide range of isotopes, leaving those of interest hidden by more abundant contaminants
We reported recently on the technical aspects of the first successful use of the Laser Ion Source and Trap (LIST) at ISOLDE for on-line production of radioisotopes from a uranium-based target with an improved laser ionization efficiency of a factor of 2.5 leading to a reduced loss of the beam of interest of only a factor of 20 [36]
Summary
The study of radioactive neutron-rich nuclei in the lead region, where Z 1⁄4 82 is a nuclear magic number, is an experimental challenge. The reaction products are extracted from the target, ionized, separated in magnetic fields, and delivered to experiments as low-energy ion beams (up to 60 keV) of a chosen isotope In a slightly modified version using a sextupole structure, it was applied to a laser ion source coupled with a gas catcher, first at the LISOL setup of the Cyclotron Research Centre (Louvain-La-Neuve, Belgium) [27] and more recently at the IGISOL facility of the University of Jyväskylä (Finland) [28,29] It has been successfully launched as a standard add-on unit for use with the hot-cavity RILIS at the thick-target radioactive ion-beam facilities ISOLDE [30,31] and TRIUMF-ISAC [32,33]. The list has enabled the first measurement of the hyperfine structure and isotope shift of 217Po and the first nuclear decay study of 219Po, which are both of interest to delineate the region of octupoledeformed nuclei [5,37]
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