ISBN 9783843934473

978-3-8439-3447-3, Reihe Physik

Claus Feuerstein
Improvement of measurement capabilities at the Cologne Accelerator Mass Spectrometer

216 Seiten, Dissertation Universität Köln (2016), Softcover, A5

Zusammenfassung / Abstract

Accelerator mass spectrometry is an extremely sensitive method for determining isotopic ratios. With CologneAMS a completely new AMS setup has been established. The 6 MV accelerator setup was designed by High Voltage Engineering Europe and installed in the Institute of Nuclear Physics at the University of Cologne in 2010.

Within the scope of this work it was possible to successfully add plutonium to the range of routinely measurable elements. This includes the development of a measurement method and the writing of a software for a semi automatic data analysis. No acceptance tests were provided for plutonium by HVEE and the special circumstances - plutonium has only rare, radioactive isotope - demand the application of techniques and procedures that have not been used for any other isotope at CologneAMS so far. For the first time the 3+ charge state is being used with a machine of this size and this results in an excellent transmission.

The isotope specific energy loss in silicon nitride foils is a common method for the suppression of isobaric interferences. In order to allow a better planning of future setups, that aim at the optimization of isobar separation, the properties (energy loss, energy loss straggling and angular straggling) of various ions in these foils have been measured using the position-sensitive time of flight spectrometer Cerberus. The results have been compared with the predictions of different theoretical models.

A gas-filled magnet is another established method for isobar separation in accelerator mass spectrometry. Its advantages are a high transmission of the wanted isotope and a good spatial separation of the isobar. The 120° magnet at the 6 MV accelerator of CologneAMS has been modified and can now also be operated in this mode. In first experiments the beam widths - which are needed for a final detector design - of various isotopes have been measured. Their transmission and therefore the gains in comparison with the foil absorption technique have also been determined. A very simple Monte Carlo simulation has been implemented, which reproduces experimental results qualitatively.