Universität zu Köln

Pfeifer, Markus (2017). The Tantalum isotope inventory of terrestrial and early solar system materials. PhD thesis, Universität zu Köln.

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Abstract

Tantalum is the rarest stable element in the solar system and consists of two stable isotopes with a huge difference in abundances (180Ta = ~0.012% and 181Ta = ~99.988%), making 180Ta the rarest stable nuclide in the solar system. Tantalum isotopes are produced together with other heavy isotopes during stellar nucleosynthesis in stars at the end of their life, in red giants as well as in supernova explosions. While 181Ta has been produced by the rapid and slow neutron capture processes (r- and s-process), the rare isotope 180Ta is bred by the branched s- process and by the special neutrino-process. Tantalum-180 is the only observationally stable nuclide in an excited nuclear state, which is why nuclear astrophysics has long searched for viable production mechanism to explain the abundance of 180Ta in the solar system. The earliest materials of the solar system carry nucleosynthetic anomalies as fingerprints of their stellar origin, thus, astrophysical models of Ta nucleosynthesis might be tested in meteorites. The low abundance of 180Ta relative to isotopes of similar mass make Ta isotope compositions to a sensitive tracer of ingrowth from nuclear reactions in neighboring elements like Hf in the early solar system. In modern geochemistry, Ta is a key trace element, belonging to the group of high field strength elements (HFSE, i.e., Zr, Nb, Hf, Ta). Due to analytical difficulties related to the low abundance of 180Ta, the absolute isotope composition of tantalum is one of the least constrained of any naturally occurring elements and possible natural variations in 180Ta/181Ta have so far not been investigated. The unusual production and physical properties of 180Ta might render Ta isotope compositions useful for tracing nucleosynthetic input or irradiation in the early solar system. Substantial analytical development allowed the evaluation of possible variations in Ta isotopes in solar system materials and whether natural Ta stable isotope variations exist on Earth.

Item Type:	Thesis (PhD thesis)
Creators:	Creators Email ORCID ORCID Put Code Pfeifer, Markus m.pfeifer@uni-koeln.de UNSPECIFIED UNSPECIFIED
URN:	urn:nbn:de:hbz:38-78804
Date:	2017
Language:	English
Faculty:	Faculty of Mathematics and Natural Sciences
Divisions:	Faculty of Mathematics and Natural Sciences > Department of Geosciences > Institute of Geology and Mineralog
Subjects:	Physics Chemistry and allied sciences Earth sciences
Uncontrolled Keywords:	Keywords Language Cosmochemistry English Nucleosynthetic anomalies English Meteorites English Calcium-Aluminum-rich inclusions English Early irradiation English Mass spectrometry English Isotope geochemistry English
Date of oral exam:	18 January 2017
Referee:	Name Academic Title Münker, Carsten Prof. Dr.
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/7881