Tantalum Isotope Anomalies in CAIs: a Vestige of Irradiation in the Early Solar System

Markus Pfeifer, Carsten Münker, Stefan T. M. Peters, Nicholas S. Lloyd

Research output: Contribution to conferenceConference Abstract


Calcium-Aluminum-rich inclusions (CAIs) record the
earliest history of our Solar System. A diversity of isotope
anomalies has been found in CAIs for a range of elements,
which is attributed to variable contributions of distinct
components synthesized at different stellar sites [1]. So far,
conventional models failed to explain the complexity in
nucleosynthetic anomalies observed in CAIS. In an approach
to identify processes acting on CAIs, and to search for exotic
nucleosynthetic anomalies for narrowing down stellar
sources, we combine high-precision high field strength
element (HFSE) concentration and isotope measurements on
6 CAIs for Hf, Ta and W. Both element concentrations (by
means of isotope dilution) and natural isotope compositions
were obtained by MC-ICP-MS at Cologne-Bonn, whereas Ta
isotope ratios were measured with a MC-ICP-MS at Thermo
Scientific, Bremen, applying newly developed 1013 Ω
resistors for Faraday cup amplifiers [2].
Tantalum isotopes show resolvable excess in 180Ta in two
of the analyzed CAIs. If these anomalies reflect
nucleosynthetic heterogeneity, it is not correlated with p-, s-,
or r-process anomalies in the neighboring elements Hf and W
[3]. Then, the Ta anomalies may express variations in
neutrino process derived nuclides, which would hint to
decoupling of p-process supernova ejecta [4]. In the light of
recent findings reporting excesses in 50V and 138La [5, 6], we
propose an early irradiation origin of the 180Ta excesses.
Minor isotopes 50V, 138La, and 180Ta are all odd-odd-isotopes
occupying interstitial sites in the chart of nuclides, where they
can be produced by (p,n) reactions on much more abundant
isotopes 50Ti, 138Ba, and 180Hf. We suggest that proton-irradiation
from the nascent sun might have been more
efficient in altering isotope compositions of certain heavy
elements than previously thought.
[1] Dauphas & Schauble (2016) Annu. Rev. Earth Planet.
Sci. 44, 709–83. [2] Pfeifer et al. (2017) J. Anal. At.
Spectrom. 32, 130-143. [3] Peters et al. (2017) Earth Planet.
Sci. Lett. 459, 70-79. [4] Rauscher et al. (2013) Rep. Prog.
Phys. 76, 066201. [5] Shen & Lee (2003) Astrophys. J. 596,
L109–L112. [6] Sossi et al. (2017) Nat. Astron. 1, 0055.
Original languageEnglish
Publication statusPublished - 1 May 2017
EventGoldschmidt 2017 - Paris, France
Duration: 13 Aug 201718 Aug 2017
Conference number: 27


ConferenceGoldschmidt 2017
Internet address


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