Thursday, 8 September 2005 - 9:50 AM

This presentation is part of: Astrophysics and Cosmochemistry II

Development of Isobar Separation for 182Hf AMS Measurements of Astrophysical Interest

Christof Vockenhuber1, Andreas Bergmaier2, Max Bichler3, Thomas Faestermann2, Susanta Lahiri4, Gunther Korschinek2, Klaus Knie2, Walter Kutschera5, Samir Maji6, Georg Rugel2, Peter Steier5, and Anton Wallner5. (1) TRIUMF, 4004 Wesbrook Mall, Vancouver, BC V6T 2A3, Canada, (2) Fakultät für Physik, Technische Universität München, Garching, D-85748, Germany, (3) Stadionallee 2, Atominstitut der Österreichischen Universitäten, Wien, A-1020, Austria, (4) 1/AF Bidhannagar, SAHA Institute of Nuclear Physics, Kolkata, 700064, India, (5) Vienna Environmental Research Accelerator (VERA), Institut für Isotopenforschung und Kernphysik, Universität Wien, Währinger Str. 17, Wien, A-1090, Austria, (6) Department of Chemistry, The University of Burdwan, Golapbag, Burdwan, 713104, India

The astrophysical interest in 182Hf (t1/2 = 8.90 ± 0.09 Myr [1]) is related to the understanding of nucleosynthesis of heavy elements in stellar environments. A high abundance of 182Hf in the early solar system was inferred based on isotopic anomalies in the stable decay product 182W found in meteorites, which challenged nucleosynthesis models, and is also useful to study time constraints in the formation of the terrestrial core and the Moon in the early solar system.

In addition to the production of 182Hf prior to the birth of our solar system, there is 182Hf production expected from ongoing nucleosynthesis. Since there is no significant natural and anthropogenic production of 182Hf on Earth, finding live 182Hf would give a strong indication of recent and nearby nucleosynthesis events. A positive signal would also help to confirm the 60Fe signal recently found in deep-sea Fe-Mn crusts [2] and to test nucleosynthesis models. 

Although AMS is well suited for search of minute amounts of 182Hf, the measurement itself is a big challenge, because of the interfering stable isobar 182W. Tungsten is a common element in laboratory environments. Due to the small difference in specific energy loss between 182Hf and 182W of a few percent, even at high ion energies (e.g. 200 MeV at the Munich MP tandem), conventional methods like an ionization chamber or a gas-filled magnet are not sufficiently selective. Thus we used a new approach based on passive absorption and time-of-flight measurement (called DeltaTOF). This method allows a suppression of the isobar 182W of about 3 orders of magnitude at the final detector. In addition, a chemical separation of Hf-W was developed, which is necessary to reduce the tungsten content in the sample to the ppm level.

Details of isobar separation at the detector and Hf-W chemistry will be discussed.

[1] C. Vockenhuber, F. Oberli, M. Bichler, I. Ahmad, G. Quitté, M. Meier, A. N. Halliday, D.-C. Lee, W. Kutschera, P. Steier, R. J. Gehrke, R. G. Helmer. Phys. Rev. Lett. 93 (2004) 172501

[2] K. Knie, G. Korschinek, T. Faestermann, E.A. Dorfi, G. Rugel, A. Wallner. Phys. Rev. Lett. 93 (2004) 171103


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