In preparation of a laser ion source, we have investigated multi-step laser ionization via Rydberg and autoionizing states for atomic Ni and Ge using a mass separator with an ion beam energy of 20 keV. For both elements resonant three-step excitation schemes suitable for modern Ti:sapphire laser systems were developed. Rydberg series in the range of principal quantum numbers 20 n 80 were localized, assigned and quantum numbers were allocated to the individual resonances. Ionization potentials (IP) were extracted from fits of the individual series and quantum defects of individual levels were analysed for confirmation of series assignment. For Ni the ionization potential could be extracted with significantly increased precision compared to literature with a value of E IP (Ni) = 61 619.77(14) cm −1. Also, at least one notable autoionizing state above the first IP was discovered for both elements, and the different ionization schemes via Rydberg or autoionizing states were compared with respect to line shape, ionization efficiency and selectivity.
Beams of short-lived radioactive nuclei are needed for frontier experimental research in nuclear structure, reactions, and astrophysics. Negatively charged radioactive ion beams have unique advantages and allow for the use of a tandem accelerator for post-acceleration, which can provide the highest beam quality and continuously variable energies. Negative ion beams can be obtained with high intensity and some unique beam purification techniques based on differences in electronegativity and chemical reactivity can be used to provide beams with high purity. This article describes the production of negative radioactive ion beams at the former holifield radioactive ion beam facility at Oak Ridge National Laboratory and at the CERN ISOLDE facility with emphasis on the development of the negative ion sources employed at these two facilities.
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