High-Precision Tantalum Isotope Measurements by MC-ICPMS

Markus Pfeifer, Carsten Münker, Stefan T. M. Peters

Research output: Contribution to conferenceConference Abstract


Tantalum-180(m) is the rarest observationally stable
nuclide in the solar system and has a relative abundance of
0.01201 ± 8% [1]. Furthermore, 180mTa is the only nuclide that
is stable in an excited state, whereas in ground state it
undergoes decay to 180Hf and 180W with a half-life of 8.1h.
Therefore, the nucleosynthetic origin of solar system 180mTa
and the relative contributions from s-process branching at
179Hf and from neutrino process in core-collapse supernovae
are uncertain [2]. Isotope analyses on natural materials may
provide a clue to the source of this nuclide. However, the
extremely low 180mTa/181Ta ratio challenges sufficiently precise
measurements. Here we present a high precision method as
well as first data on extraterrestrial material.
Tantalum from two basalts (La Palma, Canary Islands)
and one L6 chondrite (Wagon Mound) was separated by anion
exchange chromatography modified after [3,4]. Measurements
were conducted with a Neptune MC-ICPMS using 1012Ω
amplifiers on masses 180 (Ta, Hf, W) and 178Hf for monitoring
the large isobaric interference by 180Hf (rel. ab. 30.64%). Tungsten-183
was monitored for correction of the minor 180W interference
(rel. ab. 0.12%). Tantalum-181 was tuned to 40-45V to achieve
optimum precision. Instrumental mass bias was corrected for
externally by doped Yb, using different ratios between masses
171 to 176 and the exponential law. This protocol enables
more precise measurements than using doped Re [4], and the
external reproducibility (20) was typically better than ±7 --
units for ca. 80ng of sample
We found that our anion exchange chromatography
procedure can efficiently separate interfering Hf and W from
Ta. Measured solutions had both Hf/Ta and W/Ta of less than
0.00002, sufficiently low to measure 180mTa/181Ta ratios
accurately. First results for the L6 chondrite and the La Palma
basalts are indistinguishable from the terrestrial isotopic value
defined by the Alfa AesarTM standard solution.
[1] de Laeter & Bukilic (2005) Phys. Rev. C 72 (2), 025801.
[2] Travaglio et al (2011) ApJ 793 (2), 93. [3] Münker et al
(2001) Geochem. Geophys. Geosyst. 12 (2), 2001GC000183.
[4] Weyer et al (2002) Chem. Geol. 187, 295.
Original languageEnglish
Publication statusPublished - 1 May 2013
EventGoldschmidt 2013 - Florence, Italy
Duration: 25 Aug 201330 Aug 2013


ConferenceGoldschmidt 2013


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