Spontaneous and photo-induced decay processes of WF5 - and HfF5 - molecular anions in a cryogenic storage ring.

Spontaneous and photo-induced decay processes of HfF5 - and WF5 - molecular anions were investigated in the Double ElectroStatic Ion Ring ExpEriment (DESIREE). The observation of these reactions over long time scales (several tens of ms) was possible due to the cryogenic temperatures (13 K) and the extremely low residual gas pressure (∼10-14 mbar) of DESIREE. For photo-induced reactions, laser wavelengths in the range 240 to 450 nm were employed. Both anion species were found to undergo spontaneous decay via electron detachment or fragmentation. After some ms, radiative cooling processes were observed to lower the probability for further decay through these processes. Photo-induced reactions indicate the existence of an energy threshold for WF5 - anions at about 3.5 eV, above which the neutralization yield increases strongly. By contrast, HfF5 - ions exhibit essentially no enhanced production of neutrals upon photon interaction, even for the highest photon energy used in this experiment (∼5.2 eV). This suppression will be highly beneficial for the efficient detection, in accelerator mass spectrometry, of the extremely rare isotope 182Hf using the 182HfF5 - anion while effectively reducing the interfering stable isobar 182W in the analyte ion 182WF5 -. The radionuclide 182Hf is of great relevance in astrophysical environments as it constitutes a potential candidate to study the events of nucleosynthesis that may have taken place in the vicinity of the solar system several million years ago.

Correction: Novel 90Sr analysis of environmental samples by Ion-Laser InterAction Mass Spectrometry.

Correction for 'Novel 90Sr analysis of environmental samples by Ion-Laser InterAction Mass Spectrometry' by Maki Honda et al., Anal. Methods, 2022, 14, 2732-2738, https://doi.org/10.1039/D2AY00604A.

Novel 90Sr analysis of environmental samples by Ion-Laser InterAction Mass Spectrometry.

The sensitive analysis of 90Sr with accelerator mass spectrometry (AMS) was developed to advance environmental radiology. One advantage of AMS is the ability to analyze environmental samples with 90Sr/88Sr atomic ratios of 10-14 in following a simple chemical separation. Three different IAEA samples with known 90Sr concentrations (moss-soil, animal bone, Syrian soil: 1 g each) were analyzed to assess the validity of the chemical separation and the AMS measurement. The 90Sr measurements were conducted on the AMS system VERA combined with the Ion Laser InterAction Mass Spectrometry (ILIAMS) setup at the University of Vienna, which has excellent isobaric separation performance. The isobaric interference of 90Zr in the 90Sr AMS was first largely removed by chemical separation. The separation factor of Zr in two-step column chromatography with Sr resin and anion exchange resin was 106. The 90Zr remaining in the sample was effectively suppressed by ILIAMS. This procedure achieved a limit of detection <0.1 mBq in the 90Sr AMS, which is lower than typical ß-ray detection. The agreement between AMS measurements and nominal values for the 90Sr concentrations of IAEA samples indicated that the new highly-sensitive 90Sr analysis in the environmental samples with AMS is reliable.

Light induced suppression of sulfur in a cesium sputter ion source.

New techniques for suppression of atomic isobars in negative ion beams are of great interest for accelerator mass spectrometry (AMS). Especially small and medium-sized facilities can significantly extend their measurement capabilities to new interesting isotopes with a technique independent of terminal voltage. In a new approach, the effect of continuous wave laser light directed towards the cathode surface in a cesium sputter ion source of the Middleton type was studied. The laser light induced a significant change in oxygen, sulfur and chlorine negative ion production from a AgCl target. Approximately 100 mW of laser light reduced the sulfur to chlorine ratio by one order of magnitude. The effect was found to depend on laser power and ion source parameters but not on the laser wavelength. The time constant of the effect varied from a few seconds up to several minutes. Experiments were first performed at the ion beam facility GUNILLA at University of Gothenburg with macroscopic amounts of sulfur. The results were then reproduced at the VERA AMS facility with chemically cleaned AgCl targets containing ∼1 ppm sulfur. The physical explanation behind the effect is still unclear. Nevertheless, the technique has been successfully applied during a regular AMS measurement of 36Cl.