Radioactive negative ions: Production and laser spectroscopy at ISOLDE

Abstract

Negative ions are fragile quantum systems in which electron correlation effects play a significant role in the binding of the extra electron to the atom or molecule. Hence, negative ions are of interest to gain insight into fundamental atomic properties by probing theory beyond the independent particle model. However, due to the shallow binding potential, the binding energy of the extra electron, referred to as electron affinity (EA) is typically the only atomic parameter which can be determined with high precision. This thesis concerns production and spectroscopy of radioactive negative ions at CERN-ISOLDE. A key result in the study of radioactive negative ions is presented with the determination of the electron affinity of astatine by means of collinear laser photodetachment spectroscopy. This experiment was performed utilising the Gothenburg ANion Detector for Affinity measurements by Laser PHotodetachment (GANDALPH), which underwent a detector upgrade to allow for operation in the UV spectrum using a novel, fully transparent graphene target. The EA of astatine was determined to be 2.415 78(7) eV, which not only serves as a milestone towards the investigation of other heavy and eventually super-heavy negative ions, but also facilitates the use of astatine in targeted radionuclide therapy of cancer by revealing some of its fundamental chemical behaviour. Furthermore, work towards the improvement of the sensitivity of laser photodetachment threshold spectroscopy was performed by utilising a Multi viii Reflection Time of Flight (MR-ToF) device. In respect to the production of radioactive negative ions, efforts have been made to increase the production efficiency and broaden the availability of negative ions at ISOLDE. As an alternative low work function surface ioniser material, SrVO3 was produced and characterised and alternatively the use of caesiated metal surfaces was explored. Furthermore, sputter type negative ion production was investigated utilising a FEBIAD type ion source as well as the modified KENIS ion source.