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Die Untersuchung zeichnet die Entwicklung von Kernforschung und Kerntechnologie in der DDR in der Zeit zwischen 1945 bis 1965 nach. Als Industriestaat in hohem Maß abhängig vom einzig verfügbaren Primärenergieträger Braunkohle, erregte die ab den 50er-Jahren technisch mögliche zivile Nutzung der Atomkraft frühzeitig die Aufmerksamkeit der Partei- und Staatsführung. Als besonderes Argument hierfür wurde das Vorhandensein größerer Uranlagerstätten auf dem Staatsterritorium gewertet. Nach einem wenig erfolgreichen ersten Anlauf unmittelbar nach der Staatsgründung wurden ab 1955 enorme Anstrengungen unternommen, in der DDR eine weitestgehend eigenständige Kernenergieindustrie zu etablieren. Doch trotz eines breiten Einsatzes materieller und personeller Ressourcen blieb der Aufbau der angestrebten eigenständigen Atomwirtschaft in den Anfängen stecken. Die 1965 gefällte Entscheidung, den Aufbau der Kernenergiewirtschaft der DDR auf der Basis sowjetischer Kerntechnik fortzusetzen, bedeutete eine grundlegende Zäsur der Kernenergiepolitik und letztlich auch das Ende der hochfliegenden Ambitionen auf eine eigenständige Kernenergiewirtschaft. Anhand von Unterlagen der Regierung der DDR, des ZK-Apparates der SED sowie der Deutschen Akademie der Wissenschaften zu Berlin zeigt die Studie die Rahmenbedingungen, Voraussetzungen und Zielsetzungen, unter denen in der DDR versucht wurde, den großtechnischen Einstieg in die Nutzung der Kernenergie zu vollziehen. Vor dem Hintergrund des Kalten Krieges und einer weltweiten „Atomeuphorie“ erfolgt eine Einbindung in den internationalen Kontext von Kernforschung und technischer Entwicklung sowie der globalpolitischen Rahmenbedingungen. Neben den enorm hohen Erwartungen an eine künftig unabhängige Energieerzeugung und eine exportorientierte Nuklearindustrie wird der Fokus auch auf die politischen Zielsetzungen gelegt, die die SED-Führung mit der breiten Entwicklung von Kernforschung und Kerntechnologie verfolgte. Dabei verknüpft der Autor die Ambitioniertheit der Planungen zur Kernenergieentwicklung mit der für die Parteiführung essentiellen Frage der internationalen Anerkennung ihres Staates und der deutsch-deutschen Konkurrenzsituation.
This thesis describes the implementation and first on-line application of a multi-reflection time-of-flight (MR-ToF) mass analyzer for high-resolution mass separation at the ISOLTRAP mass spectrometer at ISOLDE/CERN. On the one hand, the major objective was to improve ISOLTRAPs mass-measurement capabilities with respect to the ratio of delivered contaminating ions to ions of interest. On the other hand, the time necessary to purify wanted from unwanted species should be reduced as much as possible to enable access to even more exotic nuclei. The device has been set up, optimized and tested at the University of Greifswald before its move to ISOLTRAP. The achieved performance comprises mass resolving powers of up to 200000 reached at observation times of 30ms and a contamination suppression of about four orders of magnitude by use of a Bradbury-Nielsen gate. With the characteristics, it outperforms clearly the so far state-of-the-art purification method of a gas-filled Penning trap. To improve the utilization of the MR-ToF mass analyzer, the in-trap lift method has been developed. It simplifies the application and optimization of the device, which is a crucial time factor in an on-line experiment. The device was the first of its kind successfully applied to radioactive ion beams for a mass analysis, for a mass separation (in combination with the Bradbury-Nielsen gate) as a preparatory step for a subsequent Penning-trap mass measurement and as a high-precision mass spectrometer of its own. The later was recently used for the first mass measurement of the neutron-rich calcium isotopes 53Ca and 54Ca. The so-far achieved mass-resolving power of 200000 belongs to the highest reported for time-of-flight mass analyzers at all. The first successful application of the MR-ToF system as the only mass separator at ISOLTRAP resulted in the mass measurement of 82Zn. The new mass value has been compared to mass extrapolations of the most recent Hartree-Fock-Bogoliubov (HFB) mass models, HFB-19 to HFB-21, of the BRUSLIB collaboration. The mass of the nuclide is of high interest for the compositions and depth profile of the outer crust of neutron stars. In the classical model of the outer crust of a cold, non-accrediting and non-rotating neutron star, the sequence of nuclides found within this parts is determined mainly by the binding energy of exotic nuclides. The crustal compositions determined with the three HFB mass models differed with respect to the appearance of a layer of 82Zn, originating from different mass extrapolations of this mass. With the new experimental data, the extrapolations could be evaluated. It was found that the HFB-21 mass value differs less from the experimental data than the ones from HFB-19 and 20. Therefore, in the classical model, 82Zn does not appear anymore in the outer crust. Due to its high resolution and very fast measurement time, the MR-ToF mass analyzer will be an important instruments for future activities at ISOLTRAP, at the ISOLDE facility in general, and at other radioactive ion-beam facilities.
Research into nuclear physics has enjoyed a long and rich history since the earliest experiments began investigating atomic constituents. The discovery of the atomic nucleus in the early 20th century started a complex field of research that has undergone many transformations with the advancements of modern technology. Today, atomic nuclei are not only studied to advance our understanding of the strong force but also to gain more information on the synthesis of elements in the universe, to exploit nuclear decay to investigate the weak interaction, and to search for physics beyond the standard model.
In this work, we will study the strong force in atomic nuclei, i.e. the way nucleons (protons and neutrons) arrange themselves in a many-body system governed by the repulsive Coulomb interaction and the attractive strong interaction. In particular, we will focus on nuclear structure near nuclei with a "magic number" of Z protons and N neutrons, so-called doubly-magic nuclei, exhibiting a particularly stable configuration with respect to neighboring nuclei.
Within the nuclear shell model, similar to the atomic shells, the magic numbers indicate shell closures accompanied by energy gaps. Nuclei at double-shell closures and their direct vicinity provide an important playground to benchmark nuclear theories and models that aim to predict the intricate interplay of the nucleons that lead to enhanced nuclear binding energies, significant changes in charge radii and transition strengths, etc.
Of particular interest are nuclear isomers, long-lived excited states, in which the nucleon configuration with respect to its ground state is altered, resulting in a modification of their properties despite having the same number of protons and neutrons.
The main part of this work consists of three publications, which report on nuclear structure investigations through mass measurements and laser spectroscopy near the doubly magic nuclei nickel-78, tin-100, and lead-208.
The nuclides investigated in this work include neutron-deficient indium isotopes, neutron-rich zinc isotopes, and neutron-rich mercury isotopes.
This work describes the recent scientific and technical achievements obtained at the high-precision Penning trap mass spectrometer SHIPTRAP. The scientific focus of the SHIPTRAP experiment are mass measurements of short-lived nuclides with proton number larger than 100. The masses of these isotopes are usually determined via extrapolations, systematic trends, predictions based on theoretical models or alpha-decay spectroscopy. In several experiments the masses of the isotopes 252-255No and 255,256Lr have been measured directly. With the obtained results the region of enhanced nuclear stability at the deformed shell closure at the neutron number 152 was investigated. Furthermore, the masses have been used to benchmark theoretical mass models. The measured masses were compared selected mass models which revealed differences between few keV/c² up to several MeV/c² depending on the investigated nuclide and model. In order to perform mass measurements on superheavy nuclei with lower production rates, the efficiency of the SHIPTRAP setup needs to be increased. Currently, the efficiency is 2% and mainly limited by the stopping- and extraction efficiency of the buffer gas cell. The stopping and extraction efficiency of the current buffer gas cell is 12%. To this end, a modified version of the buffer gas cell was developed and characterized with 223Ra ion source. Besides a larger stopping volume and a coaxial injection the new buffer gas cell is operated at a temperature of 40K. The operation at cryogenic temperatures increases the cleanliness of the buffer gas. From extraction measurements and simulations an overall efficiency of 62(3)% was determined which results in an increase by a factor of 5 in comparison to the current buffer gas cell. Aside from high-precision mass measurements of heavy radionuclides the mass differences of metastable isobars was measured to identify candidates for the neutrinoless double-electron capture. Neutrinoless double-electron capture can only occur if the neutrino is its own antiparticle and a physics beyond the standard model exists since the neutrinoless double-electron capture violates the conservation of the lepton number. Due to its expected long half-life this decay has not yet been observed. However, the decay rate is resonantly enhanced if mother and daughter nuclide are degenerate in energy. Suitable candidates for the search of the neutrinoless double-electron capture have been identified with mass difference measurements uncertainties of about 100eV/c². In this work the results of the mass difference measurements of 12 possible candidates are presented.