A four-crystal monochromator beamline will be part of the radiometry l
aboratory that the Physikalisch-Technische Bundesanstalt will install
at the new storage ring BESSY II. The most important design criteria f
or the beamline are the tunability of the photon energy in a wide spec
tral range from 1.75 to 10 keV; the high spectral purity of the radiat
ion, as well as the good reproducibility of the absolute photon flux.