The Parallel Beam Diffractometer laboratory is a highly-controlled space (0.01 degree C stability) containing a set of absolutely calibrated stacked goniometer stages which are the platform for precision measurement of diffraction angles. It is used to establish lattice constants of SRM powders, and to measure X-ray wavelengths with unprecedented accuracy, in a way directly traceable to the SI definition of the second. In the past few years, the instrument has been brought into full operation, with publications describing its angular calibration and alignment (compensation of short-period errors, long-period errors and alignment).
A new project being developed is a robotic sample changer which will allow us to individually certify SRMs for which this is important. The first application will be a more precise certification of SRM 2000, a single-crystal silicon substrate with a SiGe overlayer.