5 Years of Ion-Laser Interaction Mass Spectrometry—status and Prospects of Isobar Suppression in Ams by Lasers

Abstract

A setup for ion-laser interaction was coupled to the state-of-the-art AMS facility VERA five years ago and its potential and applicability as a new means of isobar suppression in accelerator mass spectrometry (AMS) has since been explored. Laser photodetachment and molecular dissociation processes of anions provide unprecedented isobar suppression factors of >1010 for several established AMS isotopes like 36Cl or 26Al and give access to new AMS isotopes like 90Sr, 135Cs or 182Hf at a 3-MV-tandem facility. Furthermore, Ion-Laser InterAction Mass Spectrometry has been proven to meet AMS requirements regarding reliability and robustness with a typical reproducibility of results of 3%. The benefits of the technique are in principle available to any AMS machine, irrespective of attainable ion beam energy. Since isobar suppression via this technique is so efficient, there often is no need for any additional element separation in the detection setup and selected nuclides may even become accessible without accelerator at all.

Developing Accelerator Mass Spectrometry Capabilities for Anthropogenic Radionuclide Analysis to Extend the Set of Oceanographic Tracers

“…Beyond that, the novel technique of Ion-Laser Interaction Mass Spectrometry (ILIAMS) (Martschini et al, 2019b) makes new radionuclides accessible at ultra-trace concentrations. First results presented here and in Martschini et al (2021) show that this technique will allow for AMS-measurements of the fission products 99 Tc, 135 Cs, and 90 Sr at environmental levels. Since these isotopes were previously inaccessible with other techniques in the general environment ( 135 Cs), required huge instrumental effort in AMS ( 99 Tc) or relied on slow and cumbersome sample preparation for radiometric detection ( 90 Sr), ILIAMS is expected to facilitate much more widespread analysis of these tracers.…”

“…The combination of SrF 3 − extraction from the ion source and ILIAMS-suppression of ZrF 3 − provides an isobaric suppression of 90 Zr of >10 10 , which is sufficient to achieve a blank value of 90 Sr/Sr ∼5 × 10 −15 on all environmental soil and bone samples tested so far (Martschini et al, 2021). Based on the addition of 1 mg of stable Sr carrier for normalization and a total detection efficiency of 4 × 10 −4 , this is equivalent to a detection limit of <0.1 mBq, i.e., 10 5 atoms of 90 Sr per sample.…”

“…In order to facilitate the necessary ionlaser interaction times, the ion beam is decelerated to an energy at eV levels inside a radiofrequency quadrupole ion guide filled with buffer gas and overlapped with a collinear laser therein. A recent review of this method and its achievements is given by Martschini et al (2021). For "standard" AMS isobaric systems like 36 Cl-36 S and 26 AlO-26 MgO, the ILIAMS-technique provides unprecedented isobar suppression of 10 11 -10 12 (Lachner et al, 2019(Lachner et al, , 2021.…”

“…Therefore, we see a potential for the application of the ILIAMS assisted AMS measurements when oceanic data far from anthropogenic sources and close to natural 135 Cs/ 133 Cs levels are needed. Based on the performance parameters regarding 135 Ba suppression and detection efficiency (Martschini et al, 2021;Wieser, A. et al in preparation), we can now estimate the amount of ocean water sample required for the analysis of 135 Cs with ILIAMS.…”

“…In comparison, first experiments with ILIAMS showed that TcF 5 − has to be used instead of TcO − for laser suppression of the isobar Ru (Martschini et al, 2021). Since Ru is among the stable elements with the lowest natural abundance with typical concentrations of 1 ppt in water and 10-100 ppt in sediment (Bekov et al, 1984), a 10 L ocean water sample or a 100 g sediment sample will both contain roughly 6 × 10 13 atoms of Ru.…”