Spectroscopy of Stable and Radioactive Negative Ions

Abstract

Negative ions are unique quantum systems which are of fundamental interest within the field of atomic physics due to the importance of the electron correlation in their creation, stability, and existence. Properties of these ions, such as the electron affinity, i.e. the binding energy of the additional electron (EA), are of importance for example within theoretical calculations, astrophysics, medical applications, antimatter studies, and accelerator mass spectrometry. This work aims to improve the understanding of negative ions and electron correlation by measuring previously not, or less precisely, known binding energies and lifetimes of both stable and radioactive negative ions by using laser photodetachment spectroscopy. In order to achieve this, several technical developments were carried out and their feasibility was demonstrated. The measurements were performed at several different facilities: ISOLDE at CERN, the Gothenburg University Negative Ion and Laser LAboratory (GUNILLA), the Double ElectroStatic Ion Ring ExpEriment (DESIREE). The results of this thesis can be divided into different categories, the first being the determinations of the EAs of 128-iodine of 3.059 052(38) eV and of 211-astatine to be 2.415 78(7) eV, marking the first ever measurements of EAs of radioactive isotopes, and thereby paving the way to future EA measurements of other elements of the periodic table. Second, high precision measurements of the EAs of cesium and rubidium have been performed at GUNILLA, utilizing a new technique: state selected detection of the residual atom in the photodetachment processes. The measured EAs were determined to be 471.5987(6) meV for cesium and 485.898(4) meV for rubidium, which are both improvements of previously determined values. This measurement technique can, if combined with the radioactive beam technique at CERN, be applied to study francium. Third, the radiative lifetimes of the excited states in rhodium have been investigated at the DESIREE facility. In addition to the two previously known bound states, a highly mixed bound state and an autodetaching state were observed. By measuring radiative lifetimes of negative ions, theoretical models within this field can be benchmarked. Fourth, the molecular dissociation process within the Radio-Frequency Quadrupole cooler and buncher (RFQcb), ISCOOL, at ISOLDE, CERN, has been investigated to determine the efficiency of producing atomic beams from molecular beams. Finally, a new non-radioactive mass separator beamline has been designed, built and commissioned at ISOLDE, CERN. This new facility will be dedicated to ion source developments, beam optics and beam manipulation studies aiming to improve ion beam quality and the performance of targetion sources during on-line operation at the ISOLDE facility.