Berlin 2014 – scientific programme

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MS: Fachverband Massenspektrometrie

MS 11: SIMS / Accelerator Mass Spectrometry and Applications 4

MS 11.7: Talk

Friday, March 21, 2014, 12:15–12:30, DO24 1.205

The upgrade of VERA for natural ²³⁶U - first results on detection efficiency and background — •Peter Steier, Joannes Lachner, Alfred Priller, Stephan Winkler, and Robin Golser — Universität Wien, Fakultät für Physik, VERA Labor, Währingerstraße 17, 1090 Wien, Österreich

Interest in the long-lived radioisotope ²³⁶U (t_1/2=23.4 million years) has significantly increased recently, due to the emergence of environmental and earth science applications. Of the AMS instruments suited, none could achieve the sensitivity to address the expected typical natural isotopic ratios on the order ²³⁶U:²³⁸U = 10⁻¹³. One major limitation is the relatively low total detection efficiency. Stripping with helium was shown to be advantageous at lower energies [1]. We have implemented this capability at VERA, which improved the yield by a factor of four. The second instrumental limitation is background caused by ²³⁵U hydrides. With our recently installed additional 90^∘ magnet, we can suppress this background by several orders of magnitude. Our first measurements indicate a new instrumental limit below ²³⁶U:²³⁸U = 10⁻¹⁴, however, improved chemical procedures are still under development to extract such pure uranium from geological samples. Measurements of anthropogenic ²³⁶U and other actinides profit from the higher sensitivity allowing for smaller samples.

[1] Vockenhuber, C., et al., The potential of He stripping in heavy ion AMS. Nucl. Instr. and Meth. in Phys. Res. B 294 (2013) 382-386.