At the ISOLDE isotope separator on-line (ISOL) radioactive ion beam facility, a wide variety of radioactive species are produced in a thick target during its bombardment by a high-energy proton beam.Isotope separation of the ionized reaction products takes place as the ion beam passes through a magnetic mass separator. Due to the large number of isobars produced, this process alone is not sufficient for many applications of the ion beam. For many ISOLDE users it is essential, or greatly preffered for the beam to be delivered with a high degree of chemical purity, and thus, an additional separation between nuclides with different proton number Z is required. The RILIS can provide this in the form of an atomic physics technique: step-wise resonance photo-ionization. By exploiting the unique electronic structure of different atomic species the RILIS provides a rapid, efficient and highly Z selective ionization process.

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