ROBL-II: A dedicated actinide beamline for X-ray spectroscopy and scattering techniques

The Rossendorf Beamline (ROBL) operates since 1999 as a single-branch, double-experiment, multi-purpose X-ray beamline for radiochemistry and materials sciences. After 13 years of successful operation, the optical components of ROBL were replaced by state-of-the-art equipment, including a LN2-cooled double-crystal/double-multilayer monochromator, and a 1.2-m double-toroid focusing mirror with Pt and Rh coatings and 1.0 µrad slope errors. Since 2015, both experimental stations belong to the Institute of Resource Ecology at HZDR and are dedicated to study actinides. In 2016, a major upgrade program started to provide additional or largely improved techniques:

(1) A five-crystal Johann-type spectrometer with variable Rowland circle of 0.5 to 1 m to measure high-energy-resolution fluorescence detection XANES, XES and RIXS [1].
(2) A new 6-circle diffractometer for powder diffraction, crystal truncation rod (CTR) and resonant anomalous X-ray reflectivity (RAXR) measurements.
(3) A large 2D detector will further support the structure analysis of materials (PXRD, single crystal diffraction, PDF analysis).
(4) A new Ge-based energy dispersive detection system with ultrafast electronics to obtain detection limits for bulk XAS near or even below 1 ppm, and automated sample feeders for room temperature and cryogenic (10 K) conditions to enable a high sample throughput.
All experiments will be available from 2020 on in a control area comprising two hutches connected by a common lock room, which allows an easy exchange of radioactive samples (alpha emitters with total activity below 185 MBq) between four experimental stations.
Furthermore, ROBL-II will significantly benefit from the new electron storage ring of the ESRF installed in 2019/2020. ROBL-II’s new source, a short bending magnet, will provide a photon flux of 1013 ph/s across a wide energy range (3 to 35 keV). The much lower vertical divergence will allow us to obtain a spot size of 30 x 70 µm2 with the toroid mirror, thereby raising the photon density by an order of magnitude as compared to the current storage ring.
The complete experimental portfolio of ROBL-II will be available to users from 2020 on, for more than 200 (24-h) days per year, establishing the key role of ROBL-II for synchrotron-based actinide chemistry, and additionally providing beamtime for fundamental chemistry, catalysis, materials and earth sciences.

[1] K. O. Kvashnina and A. C. Scheinost, Journal of Synchrotron Radiation 2016, 23, 836-841.