Prof. Dr. Horst Geckeis
Dr. Jörg Rothe
Dr. Kathy Dardenne

Work description

For some selected aqueous systems (e.g., the Neptunium(IV) aquo-ion Np(IV)aq, which tends to be oxidized to the trans-dioxo Np(V)O2+ cation in the presence of an intense synchrotron X-ray beam), beam induced speciation changes will be investigated by controlling and systematically changing the relevant experimental parameters:

• Metal cation concentration
• Total photon flux
• Photon flux density (focused/defocused beam)
• Sample temperature (from room to liquid nitrogen temperature)
• Exposure time to the beam
• Ground state electronic level (K- vs. L- / L- vs. M-edge)
• Conditions for recovery of the pristine state before irradiation

These investigations will include a precise determination of the beam induced temperature increase (deposited energy) in the sample vial (“beam damage” might be actually a temperature induced speciation change) as well as EXAFS studies of the effect of deep freezing on the “aqueous” speciation.

Methods:

• XAFS spectroscopy at well-defined conditions in transmission / fluorescence detection mode at the INE and ACT beamline stations (coop. INE beamline group)
• Sample preparation (coop. INE aquatic chemistry group)
• XAFS data analysis  

More details