The surface preparation of beryl crystals for X-ray spectroscopy

One of the few crystals available for X-ray spectroscopy in the 1.0 to 1.5 nm band is natural beryl. This report describes work carried out to measure and improve the X-ray characteristics of four samples of the pink form of beryl (morganite) to establish the suitability of its use in the X-ray polychromator (XRP) instrument flown in the NASA Solar Maximum Mission satellite. Surface preparation of beryl crystals by etching in hydrofluoric acid followed by polishing in X-30 syton is shown to bring the rocking curve widths (FWHM) as measured on a two-crystal spectrometer to the near perfect values of 5 arc sec at Cu K alpha (0.154 nm) and 3.3 arc min at Cu L alpha (1.331 nm). In addition the crystals peak reflectivity can be enhanced by a factor eight times that of flat and ground but otherwise untreated crystals.