Installation and operation of a high-temperature surface ion source for the online coupling of TRIGA-SPEC to the TRIGA Mainz research reactor and high-precision mass measurements of transuranium nuclides at TRIGA-TRAP

Das TRIGA-SPEC Experiment ist für hochpräzise Messungen von Grundzustandseigenschaften exotischer Nuklide, wie Spaltprodukte oder Transurane, ausgelegt. Für die online-Anbindung von TRIGA-SPEC an den TRIGA Mainz Forschungsreaktor müssen die Spaltprodukte mittels eines Gas-Jet Systems aus einer Targetkammer nahe dem Reaktorkern zu einer Ionenquelle transportiert werden, welche die angebundenen Experimente mit einem radioaktiven Ionenstrahl für die eigentlichen Messungen versorgt. Design, Aufbau und Betrieb der online-Ionenquelle war ein Hauptteil der vorliegenden Arbeit. Zusätzlich wurden Untersuchungen bezüglich der optimalen Bedingungen des Gas-Jet Systems für einen zuverlässigen Ionenquellenbetrieb durchgeführt und die Ankopplung der Ionenquelle an die weiteren Elemente der Strahlstrecke vorgenommen. Der zweite Teil dieser Arbeit beschäftigt sich mit hochpräzisen Massenmessungen von Transuranen mit dem Penningfallen-Massenspektrometer TRIGA-TRAP, das einen der beiden Zweige von TRIGA-SPEC bildet. Diese Messungen tragen zur Vermessung der Region der Nuklidkarte um den deformierten Schalenabschluss bei N = 152 bei. Die Massen einiger der untersuchten Nuklide wurden zum ersten Mal direkt gemessen. Aufgrund des Auftretens von systematischen Unstimmigkeiten während der Auswertung der Massenmessungen wurde der Fokus im abschließenden Teil dieser Arbeit auf die Identifizierung und Korrektur der Quellen der beobachteten Unstimmigkeiten gelegt.The TRIGA-SPEC setup is dedicated for high-precision measurements of ground-state properties of exotic nuclides, like fission products or transuranium nuclides. For the online coupling of TRIGA-SPEC to the TRIGA Mainz research reactor, fission products are transported from a target chamber close to the reactor core by a gas-jet system to an ion source, which provides the connected experiments with a radioactive ion beam for the actual measurements. The design, installation and operation of the online ion source was a major part of the work described in this thesis. In addition, investigations on the optimal conditions of the gas-jet system for a reliable ion source operation were performed and the coupling of the ion source part to the subsequent elements of the beamline was conducted. The second part of this thesis deals with high-precision mass measurements on transuranium nuclides with the Penning-trap mass spectrometer TRIGA-TRAP, which is one branch of the TRIGA-SPEC setup. These measurements contribute to a mapping of the region of the chart of nuclides around the deformed shell closure at N = 152. The masses of some of the investigated nuclides are directly measured for the first time. Due to the appearance of systematic inconsistencies during the evaluation of the mass measurements, the focus of the final section of this thesis lies in the identification and correction of the sources of the observed inconsistencies.

Status and developments of target production for research on heavy and superheavy nuclei and elements

We give an overview of the special challenges regarding target development and production for accelerator-based heavy and superheavy-nuclei experiments in the past and perspectives for the future. Production of ever heavier elements, studies of heavy-element production in fusion or transfer reactions, spectroscopic investigations on their nuclear structure and decay and on the fission processes with fragment analyses, laser spectroscopic studies of their atomic structure, high-precision mass measurements as well as chemical studies are lively fields of current science. The ever-increasing beam intensities, feasible with new accelerator development, are crucial for the synthesis of superheavy elements because of the low cross sections for many of the reactions. Therefore, the development of target and backing materials with higher durability and experiment lifetime is increasingly important. Here we concentrate on the techniques necessary for the production of targets that are needed for experiments in this special field of interest. For the future, also development on target monitoring, target cooling, and beam intensity profile shaping techniques will play an important role, but are not in the focus of this article

Development of a recoil ion source providing slow Th ions including 229(m)^{229(m)}Th in a broad charge state distribution

Ions of the isomer $^{229m}$Th are a topic of high interest for the construction of a "nuclear clock" and in the field of fundamental physics for testing symmetries of nature. They can be efficiently captured in Paul traps which are ideal for performing high precision quantum logic spectroscopy. Trapping and identification of long-lived $^{232}$Th$^{+}$ ions from a laser ablation source was already demonstrated by the TACTICa collaboration on Trapping And Cooling of Thorium Ions with Calcium. The $^{229m}$Th is most easily accessible as $\alpha$-decay daughter of the decay of $^{233}$U. We report on the development of a source for slow Th ions, including $^{229(m)}$Th for the TACTICa experiment. The $^{229(m)}$Th source is currently under construction and comprises a $^{233}$U monolayer, from which $^{229(m)}$Th ions recoil. These are decelerated in an electric field. Conservation of the full initial charge state distribution of the $^{229(m)}$Th recoil ions is one of the unique features of this source. We present ion-flight simulations for our adopted layout and give a final design. This source will provide Th ions in their original charge state at energies suitable for capture in a linear Paul trap for spectroscopy investigations.Comment: 6 pages, 3 figures, PLATAN19 conference proceeding published in Hyperfine Interact 202

Catching, trapping and in-situ-identification of thorium ions inside Coulomb crystals of 40^{40}Ca+^+ ions

Thorium ions exhibit unique nuclear properties with high relevance for testing symmetries of nature, and Paul traps feature an ideal experimental platform for performing high precision quantum logic spectroscopy. Loading of stable or long-lived isotopes is well-established and relies on ionization from an atomic beam. A different approach allows trapping short-lived isotopes available as alpha-decay daughters, which recoil from a thin sample of the precursor nuclide. A prominent example is the short-lived $^{229\text{m}}$Th, populated in a decay of long-lived $^{233}$U. Here, ions are provided by an external source and are decelerated to be available for trapping. Such setups offer the option to trap various isotopes and charge states of thorium. Investigating this complex procedure, we demonstrate the observation of single $^{232}$Th$^+$ ions trapped, embedded into and sympathetically cooled via Coulomb interactions by co-trapped $^{40}$Ca$^+$ ions. Furthermore, we discuss different options for a non-destructive identification of the sympathetically cooled thorium ions in the trap, and describe in detail our chosen experimental method, identifying mass and charge of thorium ions from the positions of calcium ions, as their fluorescence is imaged on a CCD camera. These findings are verified by means of a time-of-flight signal when extracting ions of different mass-to-charge ratio from the Paul trap and steering them into a detector

Actinide and lanthanide thin-layer developments using a drop-on-demand printing system

Actinide and lanthanide thin layers with specific requirements regarding thickness, homogeneity, chemical purity, mechanical stability, and backing properties are applied in a multitude of physics and chemistry experiments. A novel target preparation method, the so-called “Drop-on-Demand” (DoD) technique, based on a commercial nanoliter (nL) dispenser is applied since a few years in the Nuclear Chemistry unit at Johannes Gutenberg University Mainz. The wetting behaviour of the nL droplets on the substrate’s surface is a key parameter determining the spatial distribution of the deposited material after evaporation. By switching from aqueous to organic solvents as well as by substrate surface modifications, the wetting behaviour can be influenced. Recent investigations on this influence and applications of the DoD method are presented. The produced actinide deposits were characterized by optical and scanning electron microscopy, by α spectroscopy as well as by radiographic imaging.peerReviewe