Ion beam analysis (IBA) and accelerator mass spectrometry (AMS) with the new 6 MV accelerator at FZ Dresden-Rossendorf

Since more than 30 years IBA is performed at the Forschungszentrum Dresden-Rossendorf (FZD) for the determination of element distributions. Due to continuous upgrades of the different experimental set-ups, we are able to routinely perform:

• Rutherford Backscattering Spectrometry (RBS) & Channeling (C-RBS)
• Nuclear Reaction Analysis (NRA)
• Elastic Recoil Detection Analysis (ERDA)
• Particle-Induced X-Ray (PIXE) and Gamma-Emission (PIGE)
Most of our applications lie within material sciences. We are able to measure non-destructively “all natural” elements, i.e. H to U; most elements with lateral, some in 3-D resolution with the following typical parameters (matrix- and analyte-depending):
• depth resolution: 0.5-30 nm
• depth range: nm-µm
• lateral resolution: few µm
• usual mapping area: 2x2 mm²
• maximum sample size: 3x10 cm² (vacuum) & “unlimited” (external beam)
• detection limits: ~10 µg/g (H); 500 µg/g – 1% (He-F); 10-100 µg/g (Na-U)
In summer 2009, our 5 MV van-de-Graaff accelerator will be replaced by a 6 MV Tandetron model [1], which is even more sophisticated than the lately installed 5 MV one in France [2]. The new accelerator will need less maintenance allowing more beam time. It might be also possible to expand from two to three 8-hour-shifts a day with the new fully automatic system. The main scientific advantages are an increased depth range by a factor of two for ERDA and improved detection limits for NRA. The high energy resolution also provides the ion optical requirements for a MeV-ion nanoprobe for selective in vivo-irradiation of cell nuclei at the nanometre-scale.
In addition, the machine will have special equipment for AMS [3]. There is a main advantage of using a high-energy accelerator for mass spectrometry: The background and interfering signals, resulting from molecular ions and ions with similar masses (e.g. isobars), are nearly completely eliminated. Thus, AMS provides much lower detection limits compared to conventional mass spectrometry (isotope ratios: 10^-10-10^-15).
In contrast to common low-energy AMS facilities, which have mainly specialized in radiocarbon analyses, the FZD-AMS is the first modern-type facility in the EU that will run at a terminal voltage of 6 MV. Especially in environmental and geosciences, the determination of long-lived (t_1/2 > 0.3 Ma) cosmogenic radionuclides like ¹⁰Be, ²⁶Al, and ³⁶Cl became more and more important within the last decades [4]. Using these nuclides dating of e.g. volcanic eruptions, rock avalanches, earth quakes, and glacier movements is possible.
References: [1] A. Gottdang et al., Nucl. Instr. and Meth. B 2002, 190, 177. [2] M.G. Klein et al., Nucl. Instr. and Meth. B 2008, 266, 1828. [3] http://www.fzd.de/ams. [4] J.C. Gosse and F.M. Phillips, Quat. Sci. Rev. 2001, 20, 1475.