Logo der Universität Wien

VERA Seminar

Chemistry and accelerator mass spectrometry – A life happily ever after?

Silke Merchel, Helmholtz-Zentrum Dresden-Rossendorf (HZDR), Dresden, Germany,
present address: Faculty of Physics, Isotope Physics, University of Vienna, Austria

Accelerator mass spectrometry (AMS) is the most sensitive analytical method to measure long-lived radionuclides. The detection limits are generally several orders of magnitude better, i.e. as low as 10-16 (radionuclide/stable nuclide), than any other mass spectrometry or decay counting method. AMS needs smaller sample sizes and measurements are finished within a few minutes to hours.

However, it is often forgotten that research projects applying AMS start with taking appropriate samples, followed by labour- and cost-intensive sample preparation. The goal can easily be described as “making the big samples (up to several kg’s) to fit in an AMS target holder (< 10 mg)”. This includes getting rid of the matrix and the troublesome isobars. By technical improvements of AMS leading to lower detection limits or better mass-and-element discrimination, sample masses can be reduced to gram-quantities instead of kg’s allowing easier, faster, and cheaper chemistry. Recent AMS developments also address very efficiently isobar elimination.

Nevertheless, some samples can contain different sources of the radionuclide-of-interest such as 10Be produced in the Earth’s atmosphere polluting the 10Be of interest produced in-situ in quartz. Hence, in this case chemistry is inevitable for cleaning the samples from the contamination. Another “mission” of chemistry might be the reduction of corresponding stable nuclides, e.g. 35,37Cl, 27Al, natFe by preceding cleaning or by gentle leaching to enhance the radionuclide/stable nuclide ratio or to minimize interfering nuclear reactions such as thermal-neutron capture on 35Cl. When applying isotope-dilution AMS to simultaneously determine the natCl content of a sample, which is an absolute requirement for surface exposure dating of Ca- or K-rich minerals, chemical sample preparation is also mandatory.

As the majority of research projects involving AMS is of true interdisciplinary character, knowledge of sample preparation is usually passed-on to (young) non-chemists. These are trained learning-by-doing to perform the chemical preparation of their own samples. Therefore, the development of “routine” AMS sample preparation needs to have a strong focus on safety and easy-to-be-trained aspects with the least opportunity for failure.

In conclusion, although new AMS technical developments for isobar suppression like the laser-negative interaction system at VERA promise to reduce elaborate chemistry in some cases, we should keep in mind that chemical knowledge will always be needed for a lot of interdisciplinary research projects.

 

Donnerstag, 28.03.2019    16:30 Uhr

Victor-Franz-Hess-Hörsaal
Währinger Str. 17 (Kavalierstrakt, Zugang durch den Hof)
1090 Wien

 Ankündigung

Universität Wien
Isotopenphysik

Währinger Str. 17
1090 Wien

T: +43-1-4277-517 01
F: +43-1-4277-9517
Universität Wien | Universitätsring 1 | 1010 Wien | T +43-1-4277-0