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Mathematisch-Naturwissenschaftliche Fakultät - Jahrgang 2017

 

Titel Production and PAC studies of 83Rb/83mKr solid state calibration sources for the KATRIN experiment
Autor Marius Lennart Arenz
Publikationsform Dissertation
Abstract The KATRIN experiment studies the tritium beta-decay kinematics to deduce the neutrino mass. The emitted electrons' kinetic energy close to the beta-spectrum's endpoint is analysed using a high-precision Magnetic Adiabatic Collimation combined with an Electrostatic (MAC-E) filter spectrometer. During these measurements, the spectrometer's retarding voltage is monitored using a nuclear standard: a well-known Conversion Electron (CE) line emitted by 83mKr. Because of their favourable properties the experiment uses substrates ion implanted with 83Rb, a generator of the desired 83mKr with considerably longer half life
The first part of this work focusses on the production of these ion implanted samples at the BONn Isotope Separator (BONIS) facility. The necessary changes to the ion source to obtain sufficient ion implantation efficacies are described. Two retarding lenses are integrated into the mass separator set-up to allow for a wide range of implantation energies and beam spot sizes.
Samples implanted with 83Rb/83mKr can not only be used for calibration purposes at the KATRIN experiment. The decay of 83Rb and 83mKr to 83Kr populate γ-γ and e-γ radiation cascades, a fundamental prerequisite for the application of the Perturbed Angular Correlation (PAC) method. This well-established technique of nuclear solid state physics measures the hyperfine interaction between the probe nucleus' Nuclear Quadrupole Moment (NQM) and an Electric Field Gradient (EFG) at the probes' lattice site. Due to the short range of the interaction, PAC measurements allow to extract information from the direct vicinity of the implanted probes.
The second part of this thesis focusses on the design and the construction of a PAC measurement apparatus for the probe nuclei 83Rb(83Kr) and 83mKr(83Kr). Only one (unpublished) work reports on the use of 83Rb(83Kr) as probe nucleus up to now. The present work will show the feasibility of PAC measurements using these new probe nuclei. The set-up's mechanical and electronic design is discussed. In particular, the application of Avalanche Photo Diodes (APDs) as detectors for low energy γ quanta and CEs in PAC measurements is explored. These detectors are used in conjunction with a custom build voltage sensitive preamplifier for a time resolution in the ns range. Finally, the substrates used for the KATRIN experiment are studied using the PAC method, giving insight into the incorporation lattice sites of 83mKr and its generator nuclide 83Rb.
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© Universitäts- und Landesbibliothek Bonn | Veröffentlicht: 13.12.2017