Radionuclide Research at the KIT Light Source

X-ray absorption spectroscopy and related techniques became indispensable methods in actinide and radionuclide research. One important motivation are studies concerning the mobilization and retention of long-lived actinides, fission and activation products in geochemical processes relevant for safety studies of a potential deep geological nuclear waste repository. Therefore, reliable synchrotron based speciation techniques are needed and developed at, e.g., the INE-Beamline and the ACT experimental station of the CAT-ACT wiggler beamline at the Karlsruhe Institute of Technology (KIT) Light Source.[1] These beamlines are dedicated to the investigation of radionuclide containing materials with activities up to 1 million times the European exemption limit by various speciation techniques. The KIT facilities offer a highly versatile infrastructure - including on-site radiochemistry laboratories with inert-gas alpha boxes and a shielded box-line - for the investigation of radioactive materials in the context of the nuclear waste disposal safety case and fundamental actinide research.
One experimental technique especially powerful to differentiate oxidation states of actinides is the recently emerged actinide (An) M4,5-edge high-energy resolution X-ray absorption near-edge structure (HR-XANES). ... mehr[2– 4] This presentation highlights the latest technological developments at the ACT station, enabling, e.g., the HR-XANES spectroscopic technique for samples with low radionuclide loading down to 1 ppm in combination with a cryogenic sample environment reducing beam-induced sample alterations.[5,6] A critical part of this development is a versatile gas tight plexiglass encasement which ensures all beam paths in the five-analyzer-crystal Johann-type X-ray emission spectrometer run within He atmosphere. Also the exchange between different experiments (HR-XANES, conventional XAFS, high-energy or wide-angle X-ray scattering, tender to hard X-ray spectroscopy) is made quick and easy. The new setup paves the way for the in-operando examination of coupled redox/solid-liquid interface reactions. It opens up the possibility for the investigation of environmental samples, such as specimens containing transuranium elements from contaminated land sites or samples from sorption and diffusion experiments were molecular scale understanding of retention mechanisms can be achieved. Furthermore, a first glance on the currently ongoing further development of the XES spectrometer “NEXT generation probe of chemical bonding properties of actinides and lanthanides” will be presented in this contribution.
Complementing the method portfolio at the INE-Beamline is the setup for “tender” X-ray spectroscopy (spectral range, ∼2−5 keV) in transmission or total fluorescence yield detection mode on the basis of a He flow cell. With this setup also highly active samples can be investigated in fluorescence mode at low energies. For the first time, Tc L3-edge measurements (∼2.677 keV) of aqueous Tc specimens are reported. This method surpasses conventional K-edge spectroscopy as a tool to differentiate Tc oxidation states and coordination environments.[7,8]
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