CartiX: Full‐field XRF instrument

• Detector: CCD back‐illuminated deep‐depletion 1,024 × 1,024 cooled to -60 to -80 °C under sealed vacuum. It is sensitive to photons in the energy range of 3 to 17 keV, limited at low energy by a 200‐μm‐thick beryllium window, and at high energy by the thickness of the charge‐sensitive layer of the CCD (~40 μm). The practical energy resolution during an analysis is 180–200 eV (Mn Kα) depending on the readout speed chosen. 
• Optic: Micro Pore Optic (MPO), 20μm × 20μm channels metalized with iridium by atomic layer deposition. The optic is placed at 50 mm from the CCD. 
• X-ray source: Two transmission target Pd X-ray tubes operated at 30 kV and 3 W, placed on opposite sides of the camera to limit topographic contrast and illumination gradients.

During an analysis, the analytical head is positioned at 25 mm from the artwork surface using a slide and either a laser distance meter, or two lasers crossing at the focal plane. In this position, the MPO is equidistant to the artwork surface and the CCD, providing the geometry required for 1:1 focusing.

The camera is driven at up to 3 fps (frames per second). A large number of short acquisitions are collected and processed with dedicated software to extract hyperspectral X‐ray data. Resulting X‐Y‐energy data cubes are saved in HDF5 format and can be analyzed using PyMca (Sole et al., 2007).

Without any post-processing of the data for deconvolution of the optic PSF, the instrument achieves a resolution of ~200 μm. Deconvolution algorithms under development have been shown to substantially improve the spatial resolution of the instrument (Sarrazin et al., 2016b).