Production of actinide atomic and molecular ion beams at CERN-ISOLDE

The Isotope Separation On-Line method is used to produce, extract, ionize and deliver a wide variety of radionuclides/radioisotopes as ion beams at the CERN-ISOLDE facility. This work investigates the application of the ISOL method towards the production of nuclides in the elusive actinide region of the nuclear chart. Actinide nuclides were produced in nuclear reactions with 1.4-GeV protons incident on a bulk target. They were extracted, delivered to different experimental stations and identified through measurements of their unique properties. The production of atomic ion beams was investigated for the elements with atomic numbers 89-94. Actinium was ionized using resonance laser ionization and delivered as an atomic ion beam, facilitating experimental studies of the isotopes $^{224−231}$Ac. The elements neptunium and plutonium were identified for the first time at ISOLDE. Extracted and mass-separated ion beam rates for $^{235−241}$Np and $^{234−241}$Pu were measured and compared with predictions from simulations. Molecular formation via injection of CF$_4$ gas was used to extract actinide nuclides in the form of molecular fluoride ion beams. Ac$^+$, AcF$^+$, and AcF$_2^+$ were identified by α- and γ-decay spectroscopy measurements as well as by time-of-flight mass measurements. Successful production of AcF$^+$ enabled the first laser spectroscopy studies of the AcF molecule. Uranium, neptunium, and plutonium molecules were observed. Molecules were also formed from the mass-separated ion beams in a helium-buffer-gas-filled radio-frequency-quadrupole cooler-buncher ion trap by reactions with residual gas impurities. Varying the interaction time in the trap was shown to affect the formation rates of molecular species, providing a method to produce molecules of interest at ambient temperature. The study of radiogenically produced species is prioritized at ISOLDE, thus technical developments often need to be pursued at "offline" facilities without direct irradiation. ISOLDE's offline 2 mass separator facility features copies of key ISOLDE infrastructure, making it ideal to develop the next generation of ion beams. To enable systematic studies of molecular formation, ionization, breakup and fundamental properties, ISOLDE's offline 2 mass separator facility has been upgraded with two new gas systems and time-resolved single-ion-counting data acquisition.