Ultrasensitive Detection of Actinides by Accelerator Mass Spectrometry

Accelerator mass spectrometry (AMS) represents an ultrasensitive technique for quantifying long-lived radionuclides. The new AMS facility DREAMS (DREsden AMS) see fig. 1 will broaden the spectrum of measurable radionuclides like ¹⁰Be, ²⁶Al, ³⁶Cl, ⁴¹Ca [1] to actinides with the setup of a new time-of-flight (TOF) beam line.
AMS is capable of quantifying isotope ratios, i.e. stable nuclides are usually measured in Faraday-cups while radionuclides are counted by detectors like an ionization chamber. In comparison to α-spectrometry a relative simple chemical sample preparation can be applied and isotopes like ²³⁹Pu and ²⁴⁰Pu can be distinguished at the detector. AMS determines ratios as low as 10^-16, thus, providing the lowest detection limit of all mass spectrometry methods [2]. For long half-lives it is also more sensitive than decay counting techniques.
We expect about 100 events in the detector for samples containing an amount of about 10⁴ to 10⁶ atoms of the radionuclide in the ion source. As an example the sensitivity limit for a ²³⁶U/U ratio is about 10^-12 [3].
This high sensitivity allows many applications from nuclear forensics, radiation protection, environmental monitoring to astrophysics. Isotopes measured by AMS are e.g. ²³⁶U, ²³⁷Np, ^{239,240,241,242,244}Pu [3].
This setup will be also used in the future analyzing geological samples with high lateral resolution – without chemical sample preparation - a so called Super-SIMS – a combination of a SIMS (Secondary Ion Mass Spectrometry) with an accelerator.

[1] Akhmadaliev, S. et al. (2012) Nucl. Instr. and Meth. in Phys. Res. B, 6 pages, doi: 10.1016/j.nimb.2012.01.053.
[2] Fifield, L.K. (2008) Quaternary Geochronology 3, 276-290.
[3] Steier, P. et al. (2010) Nucl. Instr. and Meth. in Phys. Res. B 268,1045-1049