In-Source Laser Resonance Ionization at ISOL Facilities

Resonance ionization laser ion source development has been carried out at two radioactive ion beam facilities: ISOLDE (CERN, Switzerland) and the IGISOL facility (Jyvaskyla, Finland). The scope of the Resonance Ionization Laser Ion Source has been extended to 27 elements with the development of new three-step ionization schemes for Sb, Sc, Dy, Y and Au. The efficiencies were determined to be in the range of 2 - 20 %. Additionally, a new two-step ionization scheme has been developed for bismuth in an off-line atomic beam unit. The scheme relies on ionization via a strong and broad auto-ionizing resonance at an energy of 63196.79 cm$^{−1}$. This scheme may offer an improvement over the existing RILIS efficiency and will be more convenient for use during resonance ionization spectroscopy of Bi isotopes. The RILIS can be used as a spectroscopic tool to probe features such as the hyperfine structures and the isotope-shifts of radioisotopes with low production rates. By coupling a laser scanning process that directly influences the initial ion creation with a detection method involving a nuclear tag, such as $\alpha$ or $\gamma$-emission, an extremely high degree of sensitivity has been achieved. A recent $^{104}$Ag ground-state and isomer measurement is presented and is an example of RILIS spectroscopy combined with $\gamma$-detection. This measurement clarifies an unusual feature observed in the hyperfine spectra during a previous study of this isotope. Recent technical improvements in the ISOLDE RILIS selectivity, laser operation and data acquisition have improved this spectroscopic technique. A description of the experimental methods and the first results of a study of the $\alpha$-emitting neutron-deficient $^{189, 191}$Bi isotopes by simultaneous atomic and nuclear spectroscopy are presented. Concerning the compatibility of the IGISOL front end with the new FURIOS laser ion source, the gas flow dynamics outside the gas cell have been investigated off-line, leading to an adaptation of the radio frequency sextupole ion guide which forms the laser/atom interaction region. The outcome of initial testing of this device is discussed.