Radioactive negative ions: Production and laser spectroscopy at ISOLDE
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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
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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.