Online chemical adsorption studies of Hg, Tl, and Pb on SiO2 and Au surfaces in preparation for chemical investigations on Cn, Nh, and Fl at TASCA

Online gas-solid adsorption studies with single-atom quantities of Hg, Tl, and Pb, the lighter homologs of the superheavy elements (SHE) copernicium (Cn, Z =112), nihonium (Nh, Z =113), and flerovium (Fl, Z =114), were carried out using short-lived radioisotopes. The interaction with Au and SiO 2 surfaces was studied and the overall chemical yield was determined. Suitable radioisotopes were produced in fusion-evaporation reactions, isolated in the gas-filled recoil separator TASCA, and flushed rapidly to an adjacent setup of two gas chromatography detector arrays covered with SiO 2 (first array) and Au (second array). While Tl and Pb adsorbed on the SiO 2 surface, Hg interacts only weakly and reached the Au-covered array. Our results contribute to elucidating the influence of relativistic effects on chemical properties of the heaviest elements by providing experimental data on these lighter homologs

Radioactive Molecular Beams at CERN-ISOLDE

The present thesis addresses aspects of molecular beam developments for thick-target radioactive ion beam facilities such as CERN-ISOLDE. At these facilities, an intense and energetic driver beam impinges on a target. Radioisotopes are produced in a target matrix from which they require to diffuse into an ion source. On their way, numerous encounters with structural materials and the target material occur, which enable desired and undesired chemical interactions. The extracted ions are separated by their mass- to-charge ratio and supplied to various experiments for investigations e.g. in nuclear structure, reactions and applications. The motivation to extract radioisotopes as molecular beams is multifold. Firstly, the elements with the highest melting and boiling points (refractory elements) require em- bedding in a volatile carrier molecule to enable their transport to the ion source. Sec- ondly, a common issue are isobaric contaminations which come along with the isotope of interest after mass separation. They can render impossible the intended user experi- ments. A powerful tool to produce and purify these beams is the extraction as molecular sideband which synthesizes volatile compounds in-situ and shifts the mass as seen by the mass separator away from the contamination. Finally, a field of investigation on radioactive molecules themselves was recently arising. This thesis is based on four publications which cover different facets of molecular beam developments. The first publication concerns the redesign and implementation of the ISOLDE yield database which provides valuable information of available beams and demonstrates the need for molecular beam developments. This implementation also contains new data and models to predict ion beam yields based on measured data. The first extraction of radioactive boron beams at a thick-target ISOL-facility is discussed in the second publication. Boron is a reactive and refractory element which cannot be extracted in elemental form. Its release properties from multi-walled carbon nanotubes are described. The measured yield of 8B is presented along with predictions for yields of 12B and 13B, based on the derived release model. As an example for beam purification by molecule formation, the third publication provides investigations by online and offline measurements towards a reliable extraction of carbonyl selenide sidebands. The investigations towards extraction of transition metals as carbonyl complexes are a major contribution to this thesis. Most of the refractory transition metals are not avail- able as ISOL beam since no suitable carrier molecules to enable their transport have been identified yet. This is often due to the harsh conditions in the target an ion source unit that typically operates at high temperatures. It was studied by simulation, calcula- tion and exploratory experiments, if carbonyl compounds could be used within a cold target concept. To avoid slow diffusion processes, the recoil momentum in fission and spallation reactions is exploited. Transition metal carbonyl compounds (e.g. Mo(CO)6) form in-situ upon their thermalization in a carbon monoxide containing atmosphere already at ambient pressure and temperature. However, these are delicate compounds which easily decompose when exposed to heat, electron bombardment or plasma. The included publication presents first exploratory experiments with an electron beam in- duced arc discharge ion source operated at ambient pressure. In contrast to classical thermionic electron production, electrons are liberated by a laser from a cold ion source. The addendum of the thesis documents experimental results towards ionization of the fragile carrier molecule Mo(CO)6 with available ISOLDE ion sources. Their ionization efficiency turned out insufficient and underlines the need for development of a cold electron impact ion source, as proposed in the publication. Moreover, an experimen- tal setup has been built and tested to study the formation of neutral transition metal carbonyl complexes at ISOLDE. The included documents describe its purpose, mode of operation and management of involved risks

Yttrium Oxide Freeze-Casts: Target Materials for Radioactive Ion Beams

Highly porous yttrium oxide is fabricated as ion beam target material in order to produce radioactive ion beams via the Isotope Separation On Line (ISOL) method. Freeze casting allows the formation of an aligned pore structure in these target materials to improve the isotope release. Aqueous suspensions containing a solid loading of 10, 15, and 20 vol% were solidified with a unidirectional freeze-casting setup. The pore size and pore structure of the yttrium oxide freeze-casts are highly affected by the amount of solid loading. The porosity ranges from 72 to 84% and the crosslinking between the aligned channels increases with increasing solid loading. Thermal aging of the final target materials shows that an operation temperature of 1400 °C for 96 h has no significant effect on the microstructure. Thermo-mechanical calculation results, based on a FLUKA simulation, are compared to measured compressive strength and forecast the mechanical integrity of the target materials during operation. Even though they were developed for the particular purpose of the production of short-lived radioactive isotopes, the yttria freeze-cast scaffolds can serve multiple other purposes, such as catalyst support frameworks or high-temperature fume filters

In-source laser spectroscopy of dysprosium isotopes at the ISOLDE-RILIS

A number of radiogenically produced dysprosium isotopes have been studied by in-source laser spectroscopy at ISOLDE using the Resonance Ionization Laser Ion Source (RILIS). Isotope shifts were measured relative to $^{152}$Dy in the 4 f$^{ 10}$6s$^{2}$ $^5$I$_8$ (gs) $\rightarrow$ 4 f$^{ 10}$6s6p (8,1)$^8_o$ (418.8 nm$_{vac}$) resonance transition. The electronic factor, F, and mass shift factor, M, were extracted and used for determining the changes in mean-squared charge radii for $^{145m}$Dy and $^{147m}$Dy for the first time.A number of radiogenically produced dysprosium isotopes have been studied by in-source laser spectroscopy at ISOLDE using the Resonance Ionization Laser Ion Source (RILIS). Isotope shifts were measured relative to $^{152}$Dy in the 4$f$$^{10}$6$s$$^{2}$ $^{5}$ I$_{8}$ (gs)→ 4$f$$^{10}$6$s$6$p$(8,1)$_{8}^{0}$ (418.8nm$_{vac}$) resonance transition. The electronic factor, $F$ , and mass shift factor, $M$ , were extracted and used for determining the changes in mean-squared charge radii for $^{145m}$Dy and $^{147m}$ Dy for the first time

The electron affinity of astatine

One of the most important properties influencing the chemical behavior of an element is the electron affinity (EA). Among the remaining elements with unknown EA is astatine, where one of its isotopes, 211At, is remarkably well suited for targeted radionuclide therapy of cancer. With the At− anion being involved in many aspects of current astatine labeling protocols, the knowledge of the electron affinity of this element is of prime importance. Here we report the measured value of the EA of astatine to be 2.41578(7) eV. This result is compared to state-of-the-art relativistic quantum mechanical calculations that incorporate both the Breit and the quantum electrodynamics (QED) corrections and the electron–electron correlation effects on the highest level that can be currently achieved for many-electron systems. The developed technique of laser-photodetachment spectroscopy of radioisotopes opens the path for future EA measurements of other radioelements such as polonium, and eventually super-heavy elements

The electron affinity of astatine

One of the most important properties influencing the chemical behavior of an element is the electron affinity (EA). Among the remaining elements with unknown EA is astatine, where one of its isotopes, 211At, is remarkably well suited for targeted radionuclide therapy of cancer. With the At− anion being involved in many aspects of current astatine labeling protocols, the knowledge of the electron affinity of this element is of prime importance. Here we report the measured value of the EA of astatine to be 2.41578(7) eV. This result is compared to state-of-the-art relativistic quantum mechanical calculations that incorporate both the Breit and the quantum electrodynamics (QED) corrections and the electron–electron correlation effects on the highest level that can be currently achieved for many-electron systems. The developed technique of laser-photodetachment spectroscopy of radioisotopes opens the path for future EA measurements of other radioelements such as polonium, and eventually super-heavy elements.peerReviewe

Opportunities for Fundamental Physics Research with Radioactive Molecules

Molecules containing short-lived, radioactive nuclei are uniquely positioned to enable a wide range of scientific discoveries in the areas of fundamental symmetries, astrophysics, nuclear structure, and chemistry. Recent advances in the ability to create, cool, and control complex molecules down to the quantum level, along with recent and upcoming advances in radioactive species production at several facilities around the world, create a compelling opportunity to coordinate and combine these efforts to bring precision measurement and control to molecules containing extreme nuclei. In this manuscript, we review the scientific case for studying radioactive molecules, discuss recent atomic, molecular, nuclear, astrophysical, and chemical advances which provide the foundation for their study, describe the facilities where these species are and will be produced, and provide an outlook for the future of this nascent field