Mass and Life-Time Measurement of the 1.7 MS $^{215}$Po Isotope A Crucial Test of the Novel Concept of the Cryogenic Ion Catcher for the Super-FRS at GSI-FAIR

Rink, Ann-Kathrin

Dissertation / PhD Thesis

GSI-2018-00736

Mass and Life-Time Measurement of the 1.7 MS $^{215}$Po Isotope A Crucial Test of the Novel Concept of the Cryogenic Ion Catcher for the Super-FRS at GSI-FAIR

Rink, A.-K.

2017

111 pp. (2017) = Dissertation, Justus-Liebig Universität Gießen, 2017

Please use a persistent id in citations: urn:nbn:de:hebis:26-opus-131139

Abstract: In modern nuclear- and nuclear astrophysics exotic nuclei are central research topics. Especially close to the driplines these nuclei show novel and unexpected properties compared to the well known stable isotopes. The obtained information from these nuclei can explore the knowledge of stellar nucleosynthesis.The international Facility for Anti-proton and Ion Research (FAIR-GSI) has the probability to provide important contributions using the Super Fragment Separator (Super-FRS). Novel experimental concepts for measurements with short-lived nuclei are presented in this thesis together with pilot experiments performed at the current Fragment Separator FRS at GSI.In the context of this doctoral thesis a method to measure very short-lived nuclei has been successfully developed. Therefore projectile fragments have been produced, separated in-flight and thermalised in a cryogenic gas-filled stopping cell. After a fast extraction the stopped projectile fragments are investigated with a high resol- ution mass spectrometer. The ion’s kinetic energy is in the order of several eV for the transport through an RFQ beam line (10−2 mbar) and maximal 1.3 keV in the analyser of the mass spectrometer. To reduce the phase space of the ions, they are either He- or N2-gas cooled.The efficient stopping of a separated exotic ion beam, produced of a 1000 MeV/u 238U projectiles, is challenging due to their large range distribution. Even though a mono-energetic degrader system reduces the range distributions, they are still bigger than the current areal gas density of the cryogenic stopping cell (CSC). An important goal for future experiments is a higher areal density to achieve the complete and thus efficient stopping of the interesting nuclei.Effects like space charge or enlarged extraction and transport times have to be minimized because they are limiting the system’s performance. If space charge is built up inside the buffer gas, the electrical transport field will be attenuated and a decrease in efficiency will be the result.In this work, extraction times of 2 ms have been achieved using a different geometry of the CSC. Important parameter dependencies on gas pressure and electrical fields have been tested with success for the next generation CSC that will be built for the Super-FRS at FAIR.The current CSC shows extraction with full efficiency up to 3 × 1011 He3+ ions produced by the incoming fragments, which corresponds an energy loss equivalent of 104 221Ac ions. Higher beam rates cause a drop in extraction efficiencies. The future CSC will provide more than three orders of magnitude higher rate capability as the current system, which enables experiments with even higher background rates. The obtained results now pave the way for the technical realization of the next generation Ion Catcher for the Super-FRS.Furthermore, a new concept has been developed to perform accurate mass and life-time measurements of the 215Po isotope. The measurements have been per- formed under conditions which are foreseen for the Low-Energy Branch of the Super- FRS [Dickel et al., 2015b]. It has been the first direct mass measurement of the 215Po isotope, even though the mass value is well known due to α-spectroscopy and system- atics. The obtained mass value of the 215Po isotope is (214.9993276 ± 8.07 · 10−05) u, which is in agreement with the literature value given by (214.9994201±2.7×10−6) u.The result of the MR-TOF-MS assisted decay spectroscopy of 215Po performed in course of this work is (1.7735 ± 0.055) ms. MR-TOF assisting decay spectroscopy simplifies the spectroscopy measurement by mass identification and separation. It also denotes that there will be no other decay channels but 215Po and its daughter decays to populate the 215Po decay channel undesirably.Concluding the experimental and simulated results evince that the new concepts for experiments at the Super-FRS are based on solid principles. A completely new generation of accurate measurements of rare isotopes are enabled.

Note: Dissertation, Justus-Liebig Universität Gießen, 2017

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