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Supervisors: Bastian Hesbacher, M.Sc., Prof. Dr. Dr. h.c. mult. Norbert Pietralla
Supervisors: Bastian Hesbacher, M.Sc., Prof. Dr. Dr. h.c. mult. Norbert Pietralla
Überprüfung phänomenologischer und mikroskopischer Modelle zur Beschreibung nuklearer Leveldichten
Examination of phenomenological and microscopic models for the description of nuclear level densities
Nuclear level densities are a central quantity in the description of statistical processes in atomic nuclei and have an important role in the modelling of nucleosynthesis.
Recently, a new experimental measurement method was developed and applied for the first time that allows to determine nuclear level densities in photonuclear reactions. For this, the method of nuclear self-absorption was employed. The experiment was conducted at the High Intensity Gamma-ray Source at Duke University, USA with the nuclide Sr-88.
This master thesis focuses on the analysis of the taken data with the objective to determine the nuclear level densities of Sr-88. Subsequently, existing phenomenological models and microscopic calculations shall be tested with the newly measured data. With this work, the student will contribute significantly to the research area for the investigation of statistical nuclear processes and provide potentially new results not existing before.
Supervisors: Dr. Johann Isaak, Prof. Dr. Dr. h.c. mult. Norbert Pietralla
Energiestabilisierung des Strahls über das Hochenergie-Scraper-System
Energy stabilization of the beam via the high-energy scraper system
The extraction beam guide of the S-DALINAC contains the high-energy scraper system. This has various slot systems that can be used to define the beam energy or to reduce the beam halo / background. The main slits – used for energy definition – have a current measurement. Via current changes on the two jaws of this system, an energy change of the beam can be detected with very fine resolution according to the very high dispersion set there. The extent to which energy changes can be transported from the accelerator hall to the extraction beamline depends on the beam dynamics set.
Within the scope of this master thesis, the current measurement on the energy-defining scraper system for stabilizing the beam energy will be set up and put into operation. Beam dynamics simulations and measurements will be used to investigate the differences between the different operating modes with the respective beam dynamics and their effects on the stabilization.
Supervisors: Dr. Michaela Arnold, Prof. Dr. Dr. h.c. mult. Norbert Pietralla
Aufbau und Inbetriebnahme eines Systems zur Stabilisierung von Strahlposition und –phase am QCLAM und LINTOTT
Setup and commissioning of a system for stabilizing beam position and phase on QCLAM and LINTOTT
For the experiments performed at S-DALINAC, the stability of the beam is of high importance. At the two electron scattering spectrometers QCLAM and LINTOTT the beam position and the beam phase should be monitored and corrected if necessary. For monitoring the beam position, a so-called OTR target would be applicable directly after the scattering target. The beam phase can be monitored non-destructively directly in front of the scattering target using a so-called high frequency monitor.
Within the scope of this master thesis, the systems for monitoring the beam position and phase will be set up and put into operation. In the process, stabilization will be set up with the aid of a closed-loop control system. Support of machine learning methods are also conceivable. Test measurements will allow a comparison between activated and non-activated beam stabilization.
Supervisors: Dr. Michaela Arnold, Prof. Dr. Dr. h.c. mult. Norbert Pietralla
Simulation und Optimierung der Phaseneinstellung für einen rezirkulierenden nicht-isochronen Strahlbetrieb am S-DALINAC
Simulation and optimization of phase adjustment for a recirculating non-isochronous beam operation at S-DALINAC
In a recirculating accelerator, the beam quality, stability and, above all, the pulse blur can be optimized by cleverly choosing the phase with which the electron bunches hit the high-frequency accelerator and the correspondingly set energy-dependent time of flight in the recirculation (longitudinal dispersion). In this process, the arcs of the three recirculations on the S-DALINAC are adjusted to achieve the desired values of longitudinal dispersion. The up to four beams in the main accelerator are set in a defined way on the flank of the high-frequency field. During the simulations, given boundary conditions such as defined momentum ratios between the different paths have to be considered as well as the adjustment possibilities due to the given beam diagnostics.
Within the scope of this master thesis, phase landscapes shall be simulated, which represent the different adjustment possibilities of the phases and longitudinal dispersions. Results and experiences of the last beam settings will be used as additional information. The stability of the obtained settings will be investigated.
Supervisors: Dr. Michaela Arnold, Prof. Dr. Dr. h.c. mult. Norbert Pietralla
Lebensdauermessung von angeregten Zuständen von Xenon-134
Lifetime measurement of excited states of Xenon-134
Supervisors: Prof. Dr. Dr. h.c. mult. Norbert Pietralla, Hannes Mayr, M.Sc.
Bestimmung des Photonenflusses mittels Uran-Spaltkammer und Compton-Monitor
Photon-flux determination using an uranium fission chamber and a Compton monitor
In nuclear photon scattering experiments, high-energy photon beams are used to excite nuclear states whose decay in the form of γ-rays can subsequently be measured with suitable detectors. In order to determine absolute measured quantities, it is necessary to know the intensity of the exciting photon beam.
Recently, an experiment was performed at the High Intensity γ-ray Source (HIγS) at the renowned Duke University in the USA. The facility generates a monoenergetic photon beam that was used to populate nuclear states at different excitation energies. The photon flux was measured in three different ways:
1) by Compton scattering of the beam at a well-defined scattering center, 2) by a uranium-238 fission chamber placed in the path of the beam, and 3) using a plastic scintillator also placed in the beam. All three measurement setups and methods provide information on the intensity of the photon beam.
In this bachelor thesis, the data from the three setups will be analyzed and compared qualitatively as well as quantitatively to determine the course of the photon flux for each series of measurements. The results of this work will thus allow the determination of absolute reaction cross sections.
Supervisors: Dr. Johann Isaak, Prof. Dr. Dr. h.c. mult. Norbert Pietralla
Untersuchung der Zählratenabhängigkeit von Lanthanbromid-Szintillationsdetektoren
Investigation of the count rate dependence of lanthanum bromide scintillation detectors
Lanthanum bromide (LaBr) scintillation detectors, with high detection efficiency and a short signal decay time, are ideal for measuring γ-spectra in nuclear physics experiments, such as nuclear resonance fluorescence experiments.
To infer the energy of γ-quanta from the pulse height of a LaBr detector signal, its energy calibration must be precisely determined. The energy calibration is usually not constant, but depends, among other things, on the detector's count rates, i.e., the number of events the detector must process within a given time period; typically 10^5 events per second.
For a recent experiment conducted at the High Intensity γ-ray Source (HIγS) at the renowned Duke University in the USA, accurate energy calibration of the LaBr detectors used is of key importance in the analysis of the measured data. As part of the experiment, several series of measurements were performed with the nucleus C-12 to determine the rate dependence of the energy calibration of the LaBr detectors. As for this bachelor thesis, the C-12 data will be analyzed to qualitatively and quantitatively determine the observed rate dependence. The results of this work are essential for the accurate analysis of the recorded experimental data.
Supervisors: Dr. Johann Isaak, Prof. Dr. Dr. h.c. mult. Norbert Pietralla
Erforschung des γ-Zerfallsverhaltens der Dipol-Riesenresonanz mittels photonuklearer Reaktionen
Probing the γ-decay behavior of the giant dipole resonance using photonuclear reactions
Photonuclear reactions play a central role in the study of the structure of atomic nuclei. For this purpose, one bombards a sample with an intense and high-energy photon beam and studies the nuclear reactions induced.
Recently, experiments on the nuclei Sm-154 and Ce-140 were successfully performed at the High Intensity γ-ray Source (HIγS) at the renowned Duke University in the USA. The aim is to investigate the decay properties of the so-called giant dipole resonance in more detail for the first time using photonuclear reactions.
In this bachelor thesis, the recorded γ-spectra will be evaluated for discrete transitions at low γ-energies. The results of this work will contribute to our understanding of the excitation and decay behavior of the giant dipole resonance.
Supervisors: Dr. Johann Isaak, Prof. Dr. Dr. h.c. mult. Norbert Pietralla
Simulation zu Justagetoleranzen von Magneten
Simulation on alignment tolerances of magnets
Each magnet in the beam guide has a defined position coming from the simulation. In reality, this positioning or even the alignment in space in general is only possible within certain tolerances. The magnetic fields in the magnets are also subject to certain tolerances.
Within the scope of this bachelor thesis, an exact investigation of the tolerances of the beam guiding elements is to be carried out with the help of simulations. On the basis of these simulations, it will be investigated how strongly which change of a beam guiding element affects the beam. The results obtained in this way will make a valuable contribution to the adjustment of the beam on the S-DALINAC.
Supervisors: Dr. Michaela Arnold, Prof. Dr. Dr. h.c. mult. Norbert Pietralla
Systematische Messung der Elektronenpaketlänge des 250 keV Elektronenstrahls
Systematic measurement of the electron bunch length of the 250 keV electron beam
An electron packet is described by a 6-dimensional phase space. The two components in the longitudinal direction (in the direction of flight) describe the length and momentum uncertainty of the electron packet. Shortly after the generation of the electron beam in the thermionic source of the S-DALINAC, a vertical diagnostic beamline provides the possibility to measure the length of the electron bunches with 250 keV kinetic energy. Up to this section there are further beam guiding elements which can influence the electron bunch length.
Within the scope of this bachelor thesis, systematic investigations of the dependence of different settings of the beam guiding on the electron bunch length shall be performed. The optimal settings for the acceleration in the superconducting injector will be verified.
Supervisors: Dr. Michaela Arnold, Prof. Dr. Dr. h.c. mult. Norbert Pietralla
Messung von Kernresonanzenergien und modellunabhängige Bestimmung von Paritätsquantenzahlen
Measurement of nuclear resonance energies and model-independent determination of parity quantum numbers
The method of nuclear resonance fluorescence is well suited for the investigation of quantum states in atomic nuclei. For this purpose, these quantum states – also called nuclear resonances – are excited by absorption of real photons. Subsequently, the γ-decay of the excited states is observed using γ-detectors (mainly high-purity germanium detectors).
A recent experiment at the High Intensity γ-ray Source (HIγS) at the prestigious Duke University in the USA is used to study magnetic and electric excitations in the isotope Mo-96
The goal of this Miniforschung is to determine, for the first time, resonance energies and parity quantum numbers of individual nuclear resonances in Mo-96 in order to separate magnetic and electric contributions in a model-independent manner.
Supervisors: Dr. Oliver Papst, Prof. Dr. Dr. h.c. mult. Norbert Pietralla
Extraktion kontinuierlicher Photoabsorptions-Wirkungsquerschnitte unter Verwendung quasi-monochromatischer Photonenquellen
Extraction of continuous photoabsorption cross sections using quasi-monochromatic photon sources
Photonuclear reactions play an important role in the study of the structure of atomic nuclei. As one of the leading groups in this research field, we systematically investigate the probability for the absorption of photons by atomic nuclei. For this purpose, real photon beams are used to determine so-called photoabsorption cross sections.
In this Miniforschung, data from experiments at the High Intensity γ-ray Source (HIγS) at the renowned Duke University in the USA will be analyzed. The aim is to determine continuous photoabsorption cross sections as a function of the excitation energy of the nucleus Te-128.
Supervisors: Dr. Johann Isaak, Prof. Dr. Dr. h.c. mult. Norbert Pietralla
Bestimmung der Aktivität einer Co-56 Quelle
Determination of the activity of a Co-56 source
The method of γ-spectroscopy, i.e. the investigation of the γ-radiation emitted by an atomic nucleus in a wide variety of reactions, allows far-reaching insights into the structure of atomic nuclei. For such investigations, among other things, the so-called detection efficiency of the corresponding γ-spectrometers must be calibrated. For this purpose, radioactive preparations with already precisely known γ-decay behavior and measured activity are usually used. A standard radioactive source used in γ-spectroscopy consists of Co-56, which decays via electron capture into the daughter nucleus Fe-56. Subsequently, γ-quanta of different energy and intensity are emitted, which are used to calibrate γ-spectrometers.
In this mini-research, the activity of a recently produced Co-56 source will be determined relative to a Co-60 source with already known activity. To do this, the γ-spectra of both sources will be measured with semiconductor detectors made of high-purity germanium and then analyzed.
Supervisors: Dr. Jörn Kleemann, Prof. Dr. Dr. h.c. mult. Norbert Pietralla
Implementierung einer Kühlwasserüberwachung an den Magnetspektrometern QCLAM/LINTOTT mit EPICS
Implementation of cooling water monitoring on the QCLAM/LINTOTT magnetic spectrometers with EPICS
The spectrometric analysis of electrons from scattering experiments, such as those performed at S-DALINAC, require the operation of dipole magnets with currents in the range of (150-300) A. In order to ensure sufficient removal of the heat generated, the dipole magnets are cooled with water. If the dipole magnets are not operated, the cooling capacity must be reduced to prevent condensation from forming inside the power supplies, which would cause corrosion and short circuits. For this purpose, a permanent temperature monitoring of the cooling water and a monitoring of the switching state of the power supply shall be implemented, which ensure that the cooling power is automatically readjusted according to the switching state of the power supply. The monitoring system shall be built with industry standard data acquisition modules and integrated and commissioned into the existing EPICS control system of the accelerator.
Learning Objectives: Digitizing analog signals from a temperature sensor, network-based readout of a device server, setting up an EPICS input/output controller, creating a graphical interface using Control-System Studio.
Prerequisite: Interest in measurement, control and regulation
Supervisors: Dr. Jonny Birkhan, Prof. Dr. Dr. h.c. mult. Norbert Pietralla
Aufbau und Charakterisierung eines NaI-Messstandes für die Freimessung von Anlagenteilen
Setup and characterization of a NaI measuring stand for the free measurement of plant components
The operation of the superconducting electron linear accelerator S-DALINAC leads to the fact that plant components are activated and thus must be treated as radioactive materials in the sense of the Radiation Protection Ordinance. In order for these plant components to be released back into the normal waste management cycle after their activity has subsided, a so-called release is required, the basis of which is a suitable measurement (clearance measurement) of the activity of these plant components. The aim of the mini-research is the construction and commissioning of a measuring station with the help of which the free measurements can be carried out. The challenge is to assemble, build and commission suitable modules for the envisaged sodium iodide detector. Then the detector system has to be calibrated and characterized. Finally, the first samples are to be measured.
Learning objectives: Digitization of analog signals from a gamma detector, operation of data acquisition modules of the NIM standard, operation of a sodium iodide detector, release procedures in radiation protection.
Prerequisites: Interest in measurement electronics for nuclear physics measurements.
Supervisors: Dr. Jonny Birkhan, Prof. Dr. Dr. h.c. mult. Norbert Pietralla
Gütemessung am S-DALINAC
Quality measurement on the S-DALINAC
A cavity resonator has a so-called quality. In simplified terms, this is a measure of how long an electromagnetic field oscillates in this cavity resonator after a single excitation. Superconducting cavity resonators (cavities) are characterized by very high Q-factors. One way to experimentally determine the Q is to measure the decay time of the excited field.
In this mini-research, the grades of cavities of the S-DALINAC will be measured and discussed. The grades of the cavities installed in the accelerator will be measured periodically so that degradations over time can be studied. Additional cavities can be measured and characterized in a vertical test cryostat.
Supervisors: Dr. Michaela Arnold, Prof. Dr. Dr. h.c. mult. Norbert Pietralla