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.

DICE: Apparatus for Detection of Internal Conversion Electrons

Peer-reviewed paper submitted as proceedings to INTDS 2022 Conference and accepted in EPJ Web Conf. Volume 285, 2023

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

The process of molecular plating and the characteristics of the produced thin films – What we have learned in 60 years and what is still unknown

Molecular plating is a well-established and widely used method for producing thin films of various elements, which are used in variety of nuclear physics applications. Sixty years have passed since the method was established, and some insights into the chemical process underlying the method and the composition of the thin films have been gained. A brief overview of what has been learned about molecular plating since its introduction and the methods applied in the characterization of molecular plated thin films is given here. Through various spectroscopic and microscopic methods, the process of molecular plating and the chemical composition are gradually being elucidated, albeit we still do not understand all aspects

Penning trap mass measurements of the deuteron and the HD+HD^{+} molecular ion

The masses of the lightest atomic nuclei and the electron mass1 are interlinked, and their values affect observables in atomic, molecular and neutrino physics, as well as metrology. The most precise values for these fundamental parameters come from Penning trap mass spectrometry, which achieves relative mass uncertainties of the order of 10−11. However, redundancy checks using data from different experiments reveal considerable inconsistencies in the masses of the proton, the deuteron and the helion (the nucleus of helium-3), suggesting that the uncertainty of these values may have been underestimated. Here we present results from absolute mass measurements of the deuteron and the HD+ molecular ion using 12C as a mass reference. Our value for the deuteron mass, 2.013553212535(17) atomic mass units, has better precision than the CODATA value by a factor of 2.4 and differs from it by 4.8 standard deviations. With a relative uncertainty of eight parts per trillion, this is the most precise mass value measured directly in atomic mass units. Furthermore, our measurement of the mass of the HD+ molecular ion, 3.021378241561(61) atomic mass units, not only allows a rigorous consistency check of our results for the masses of the deuteron (this work) and the proton, but also establishes an additional link for the masses of tritium9 and helium-3 (ref. 10) to the atomic mass unit. Combined with a recent measurement of the deuteron-to-proton mass ratio, the uncertainty of the reference value of the proton mass can be reduced by a factor of three

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

Trapping and sympathetic cooling of single thorium ions for spectroscopy

Precision optical spectroscopy of exotic ions reveals accurate information about nuclear properties such as charge radii and magnetic and quadrupole moments. Thorium ions exhibit unique nuclear properties with high relevance for testing symmetries of nature. We report loading and trapping of single $^{232}$Th$^+$ ions in a linear Paul trap, embedded into and sympathetically cooled by small crystals of trapped $^{40}$Ca$^+$ ions. Trapped Th ions are identified in a non-destructive manner from the voids in the laser-induced Ca fluorescence pattern emitted by the crystal, and alternatively, by means of a time-of-flight signal when extracting ions from the Paul trap and steering them into an external detector. We have loaded and handled a total of 231 individual Th ions. We reach a time-of-flight detection efficiency of $\gtrsim 95\, \%$, consistent with the quantum efficiency of the detector. The sympathetic cooling technique is expected to be applicable for other isotopes and various charge states of Th e.g., for future studies of $^{229m}$Th.Comment: 5 pages, 4 figure

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