Quadrupole moments of odd-A ⁵³⁻⁶³Mn: Onset of collectivity towards N = 40

The spectroscopic quadrupole moments of the odd–even Mn isotopes between N=28 and N=38 have been measured using bunched-beam collinear laser spectroscopy at ISOLDE, CERN. In order to increase sensitivity to the quadrupole interaction, the measurements have been done using a transition in the ion rather than in the atom, with the additional advantage of better spectroscopic efficiency. Since the chosen transition is from a metastable state, optical pumping in ISOLDE’s cooler and buncher (ISCOOL) was used to populate this state. The extracted quadrupole moments are compared to large-scale shell model predictions using three effective interactions, GXPF1A, LNPS and modified A3DA. The inclusion of both the 1νg9/2and 2νd5/2orbitals in the model space is shown to be necessary to reproduce the observed increase in the quadrupole deformation from N=36 onwards. Specifically, the inclusion of the 2νd5/2orbital induces an increase in neutron and proton excitations across the reduced gaps at N=40and Z=28, leading to an increase in deformation above N=36

The health impacts of energy performance investments in low-income areas: a mixed-methods approach

The study found improvements in subjective well-being and a number of psychosocial outcomes, but there was no evidence of changes in physical health

Applied Laser Spectroscopy for Nuclear Physics:Isotope Shifts in the Mercury Isotopic Chain and Laser Ion Source Development

This thesis explores two distinct applications of laser spectroscopy: the study of nuclear ground state properties, and element selective radioactive ion beam production. It also presents the methods and results of an investigation into isotope shifts in the mercury isotopic chain. These Resonance Ionization Laser Ion Source (RILIS) developments are detailed, together with an RILIS ionization scheme that allowed laser ionized ion beams of chromium, germanium, radium and tellurium to be generated at the Isotope Mass Separator On-Line (ISOLDE) facility. A combination of laser spectroscopy with decay spectroscopy and mass spectrometry unambiguously demonstrated a cessation of the extreme shape staggering first observed in the 1970s and revealed the characteristic kink at the crossing of the N=126 shell closure. A series of RILIS developments were required to facilitate this experiment, including mercury “ionization scheme” development and the coupling of the RILIS with an arc discharge ion source.Laser spectroscopy has since become a powerful tool for nuclear physics and the Resonance Ionization Laser Ion Source (RILIS), of the ISOLDE facility at CERN, is a prime example. Highlighting important advances in this field, the thesis offers a unique and revealing resource

Developments of the ISOLDE RILIS for radioactive ion beam production and the results of their application in the study of exotic mercury isotopes

This work centres around development and applications of the Resonance Ionization Laser Ion Source (RILIS) of the ISOLDE radioactive ion beam facility based at CERN. The RILIS applies step-wise resonance photo-ionization, to achieve an unparalleled degree of element selectivity, without compromising on ion source efficiency. Because of this, it has become the most commonly used ion source at ISOLDE, operating for up to 75% of ISOLDE experiments. In addition to its normal application as an ion source, the RILIS can be exploited as a spectroscopic tool for the study of nuclear ground state and isomer properties, by resolving the influence of nuclear parameters on the atomic energy levels of the ionization scheme. There are two avenues of development by which to widen the applicability of the RILIS: laser ionization scheme development, enabling new or more efficient laser ionized ion beams and the development of new laser-atom interaction regions. New ionization schemes for chromium, tellurium, germanium, mercury and radium have been determined. Additionally, for the first time, the anode cavity of the VADIS, ISOLDE's variant of the FEBIAD type arc discharge ion source was used as the laser-atom interaction region. A new element selective RILIS mode of operation was established, enabling the ISOLDE RILIS to be coupled with molten targets for the first time, increasing the flexibility of ISOLDE operation and opening a direction for future developments. This combined ion source was termed the VADLIS or Versatile Arc Discharge and Laser Ion Source. A combination of the developments presented in this thesis: an improvement of the laser ionization efficiency and the ability to couple the RILIS with molten targets, satisfied the pre-requisites for the long-awaited extension of the laser spectroscopy studies of exotic mercury isotopes. A sudden onset of extreme shape staggering in the neutron deficient mercury isotopes was revealed by optical pumping and laser spectroscopy experiments at ISOLDE in the 1970s and 1980s, with measurements conducted down to $^{181}$Hg. Despite this being one of the most remarkable examples of shape coexistence in the nuclear chart, in the intervening decades the cessation point of this odd-even staggering had yet to be unambiguously determined through measurements of nuclear ground state charge radii. This open question was successfully resolved using the ISOLDE RILIS for in-source resonance ionization spectroscopy. The experiment was performed as part of a large collaboration, using the Leuven Windmill system for α-detection; direct ion counting with the ISOLTRAP multi-reflection time-of-fight mass spectrometer (MR-ToF MS); and ion beam current measurements using the ISOLDE Faraday cups. The sensitivity of the technique enabled the measurements to be extended down to $^{177}$Hg, providing a definitive answer, that the extreme shape staggering stops at $^{180}$Hg. In addition to extending the measurements at the neutron deficient end of the mercury isotope chain, the relative mean square charge radii of both $^{207}$Hg and $^{208}$Hg was determined. This extended the measurements beyond the N = 126 shell closure, enabling the characterization of the “kink” in the trend of the isotope shifts

Ion beam production and study of radioactive isotopes with the laser ion source at ISOLDE

At ISOLDE the majority of radioactive ion beams are produced using the resonance ionization laser ion source (RILIS). This ion source is based on resonant excitation of atomic transitions by wavelength tunable laser radiation. Since its installation at the ISOLDE facility in 1994, the RILIS laser setup has been developed into a versatile remotely operated laser system comprising state-of–the-art solid state and dye lasers capable of generating multiple high quality laser beams at any wavelength in the range of 210–950 nm. A continuous programme of atomic ionization scheme development at CERN and at other laboratories has gradually increased the number of RILIS-ionized elements. At present, isotopes of 40 different elements have been selectively laser-ionized by the ISOLDE RILIS. Studies related to the optimization of the laser–atom interaction environment have yielded new laser ion source types: the laser ion source and trap and the versatile arc discharge and laser ion source. Depending on the specific experimental requirements for beam purity or versatility to switch between different ionization mechanisms, these may offer a favourable alternative to the standard hot metal cavity configuration. In addition to its main purpose of ion beam production, the RILIS is used for laser spectroscopy of radioisotopes. In an ongoing experimental campaign the isotope shifts and hyperfine structure of long isotopic chains have been measured by the extremely sensitive in-source laser spectroscopy method. The studies performed in the lead region were focused on nuclear deformation and shape coexistence effects around the closed proton shell Z = 82. The paper describes the functional principles of the RILIS, the current status of the laser system and demonstrated capabilities for the production of different ion beams including the high-resolution studies of short-lived isotopes and other applications of RILIS lasers for ISOLDE experiments

UCx target production at TRIUMF in the ARIEL era

The Advanced Rare IsotopE Laboratory (ARIEL) will increase TRIUMF’s radioactive ion beam capabilities. As part of the ARIEL target material research and development campaign, a new method to produce targets of mixed uranium carbide with excess graphite has been proposed and tested. The resulting material is comparable in composition with the conventional target material and is produced ten times faster. The reduction in production time will liberate the resources and equipment for research and development leading to new target materials with improved radioisotope release properties for ARIEL

Development of a Proton-to-Neutron Converter for Radioisotope Production at ISAC-TRIUMF

At ISAC-TRIUMF, a 500 MeV proton beam is impinged upon thick targets to induce nuclear reactions to pro-duce reaction products that are delivered as a Radioactive Ion Beam (RIB) to experiments. Uranium carbide is among the most commonly used target materials which produces a vast radionuclide inventory coming from both spallation and fission- events. This can also represent a major limitation for the successful delivery of certain RIBs to experiments since, for a given mass, many isobar-ic isotopes are to be filtered by the dipole mass separator. These contaminants can exceed the yield of the isotope of interest by orders of magnitude, often causing a significant reduction in the sensitivity of experiments or even making them impossible. The design of a 50 kW proton-to-neutron (p2n) converter-target is ongoing to enhance the production of neutron-rich nuclei while significantly reducing the rate of neutron-deficient contaminants. The converter is made out of a bulk tungsten block which converts proton beams into neutrons through spallation. The neutrons, in turn, induce pure fission in an upstream UCx target. The present target design and the service infrastructure needed for its operation will be discussed in this paper.At ISAC-TRIUMF, a 500 MeV proton beam is impinged upon “thick” targets to induce nuclear reactions to produce reaction products that are delivered as a Radioactive Ion Beam (RIB) to experiments. Uranium carbide is among the most commonly used target materials which produces a vast radionuclide inventory coming from both spallation and fission-events. This can also represent a major limitation for the successful delivery of certain RIBs to experiments since, for a given mass, many isobaric isotopes are to be filtered by the dipole mass separator. These contaminants can exceed the yield of the isotope of interest by orders of magnitude, often causing a significant reduction in the sensitivity of experiments or even making them impossible. The design of a 50 kW proton-to-neutron (p2n) converter-target is ongoing to enhance the production of neutron-rich nuclei while significantly reducing the rate of neutron-deficient contaminants. The converter is made out of a bulk tungsten block which converts proton beams into neutrons through spallation. The neutrons, in turn, induce pure fission in an upstream UCx target. The present target design and the service infra-structure needed for its operation will be discussed in this paper