Radium ionization scheme development: The first observed autoionizing states and optical pumping effects in the hot cavity environment

Highlights: • An investigation of multi-resonance photo-ionization schemes for atomic radium. • The first observation of autoionizing states of atomic radium. • The optimal of the identified schemes employs a series of five atomic transitions. • A factor of 3.8 enhancement in ionization efficiency. • Laser ionized radium ion beams are now available at the CERN-ISOLDE Facility. This paper reports on resonance ionization scheme development for the production of exotic radium ion beams with the Resonance Ionization Laser Ion Source (RILIS) of the CERN-ISOLDE radioactive ion beam facility. During the study, autoionizing states of atomic radium were observed for the first time. Three ionization schemes were identified, originating from the 7s^{2 1}S₀ atomic ground state. The optimal of the identified ionization schemes involves five atomic transitions, four of which are induced by three resonantly tuned lasers. This is the first hot cavity RILIS ionization scheme to employ optical pumping effects. The details of the spectroscopic studies are described and the new ionization schemes are summarized.