XRD1 Beamline Description

Monochromator

A Si(111) double-crystal fixed-exit monochromator, in parallel non-dispersive mode, is used to select a specific energy in the range between 4 and 21 keV, with a resolution of few eV. Crystals are cryogenically cooled by means of a LN2 closed loop system (Bruker). Parallelism of the surfaces of the two crystals is guaranteed by a piezoelectric stage acting on the second crystal: a rapid feedback loop using a downstream 4-quadrant ionization chamber maintains the flux intensity at the maximum. The monochromator is routinely calibrated via the absorption edge from fluorescence signal of reference materials (routinely iron/selenium/molibdenum edges) and the diffraction from NIST standards (usually LaB₆).