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

Advanced chemical investigations of the volatile element flerovium (Fl, Z=114)

The chemical and physical properties of transactinide elements are strongly influenced by relativistic effects. The determination of chemical properties of element 114 (flerovium, Fl) is a topic of high interest. Early atomic calculations indicated that Fl could be chemically inert. Recent relativistic calculations confirm that it should be more inert than its lighter homolog Pb, but nevertheless predict it to have a distinct metallic character. Experimental studies on Fl are challenging, due to its low production rates and relatively short half-lives. First chemistry experiments could not clarify the chemical properties due to limited statistics and inconsistent results. Therefore advanced studies on Fl were conducted at GSI, Darmstadt using TASCA. Prior to further investigations, several improvements to the experimental set-up were performed, mainly to optimize the overall efficiency and transportation time. This was assessed in multiple experiments with short-lived Hg and Pb isotopes. After the preparatory experiments, two successful Fl studies were performed at TASCA. Several radioactive decays of Fl were observed. In this thesis the details, methods and results of the experiments are discussed.Die Bestimmung der chemischen Eigenschaften von Flerovium (Fl, Z=114) ist sowohl für die theoretische als auch für die experimentelle Forschung von großem Interesse. Aufgrund der relativistischen Stabilisierung der quasi-geschlossenen Elektronenschalenkonfiguration von Fl sagten frühe theoretische Berechnungen voraus, dass Fl chemisch inert sei. Neuere realtivistische Berechnungen besagen ebenfalls ein weniger reaktives Verhalten als sein leichteres Homolog Pb, es soll aber dennoch einen ausgeprägten metallischen Charakter aufweisen. Experimentelle Studien zu Fl sind aufgrund der geringen Produktionsraten und der relativ kurzen Halbwertszeiten eine Herausforderung. Erste Experimente konnten aufgrund von widersprüchlichen Schlussfol- gerungen keine eindeutige Klärung herbeiführen. Aus diesem Grund, wurden an der GSI in Darmstadt verbesserte Experimente an TASCA durchgeführt. Zunächst wurde der Versuchsaufbau optimiert um die chemische Effizienz zu maximieren und die Transportzeit zu minimieren. Die Optimierungen wurden anhand von kurzlebigen Isotopen von Hg und Pb getestet. Nach den vorbereitenden Experimenten, wurden zwei erfolgreiche Fl-Studien an TASCA durchgeführt. Es wurden mehrere radioaktive Zerfälle von Fl beobachtet. In dieser Arbeit werden die Details, Methoden und Ergebnisse der Experimente diskutiert

First on-line detection of radioactive fission isotopes produced by laser-accelerated protons

The on-going developments in laser acceleration of protons and light ions, as well as the production of strong bursts of neutrons and multi-[Formula: see text] photons by secondary processes now provide a basis for novel high-flux nuclear physics experiments. While the maximum energy of protons resulting from Target Normal Sheath Acceleration is presently still limited to around [Formula: see text], the generated proton peak flux within the short laser-accelerated bunches can already today exceed the values achievable at the most advanced conventional accelerators by orders of magnitude. This paper consists of two parts covering the scientific motivation and relevance of such experiments and a first proof-of-principle demonstration. In the presented experiment pulses of [Formula: see text] at [Formula: see text] duration from the PHELIX laser produced more than [Formula: see text] protons with energies above [Formula: see text] in a bunch of sub-nanosecond duration. They were used to induce fission in foil targets made of natural uranium. To make use of the nonpareil flux, these targets have to be very close to the laser acceleration source, since the particle density within the bunch is strongly affected by Coulomb explosion and the velocity differences between ions of different energy. The main challenge for nuclear detection with high-purity germanium detectors is given by the strong electromagnetic pulse caused by the laser-matter interaction close to the laser acceleration source. This was mitigated by utilizing fast transport of the fission products by a gas flow to a carbon filter, where the [Formula: see text]-rays were registered. The identified nuclides include those that have half-lives down to [Formula: see text]. These results demonstrate the capability to produce, extract, and detect short-lived reaction products under the demanding experimental condition imposed by the high-power laser interaction. The approach promotes research towards relevant nuclear astrophysical studies at conditions currently only accessible at nuclear high energy density laser facilities

Rapid extraction of short-lived isotopes from a buffer gas cell for use in gas-phase chemistry experiments, Part II: On-line studies with short-lived accelerator-produced radionuclides

A novel combination of advanced gas-chromatography and detection systems coupled to a buffer-gas cell was characterized on-line to allow gas-phase chemical studies of accelerator-produced short-lived α-decaying mercury, francium, and astatine isotopes. These were produced in 40Ar- and 48Ca-induced nuclear fusion–evaporation reactions, subsequently isolated in the recoil separators MARS at Texas A&M University, USA, and TASCA at GSI Darmstadt, Germany, before being thermalized in a buffer-gas-stopping cell. From the latter, the nuclear reaction products were extracted into gas-phase chromatographic systems, suitable for registering α-decaying short-lived radionuclides, such as isotopes of superheavy elements. Efficiencies of 21(3)% for 204-209Fr were reached for the extraction into the optimized miniCOMPACT gas-chromatography setup, indicating that this technique enables the identification of isotopes of volatile as well as non-volatile elements. These studies guide the path towards chemical investigations of superheavy elements beyond flerovium, which are out of reach with currently used setups