It has been recognized that more nearly perfect crystal surfaces have a low intensity of X-ray reflection as a result of extinction effects. Therefore, it has been common practice to abrade analyzer crystals used in X-ray fluorescence analysis so that they approximate so-called mosaic crystals.
While investigating the intensity of reflection from various ADP crystals about 10 years ago, one of the authors (A) and his colleague discovered that wavelength dependence of the intensity of reflection widely varied among crystals. in other words, crystals that had a high reflection intensity for short wavelengths displayed a low reflection intensity for long wavelengths, and crystals effective for long wavelengths were not effective for short wavelengths. Also, they discovered that this phenomenon was related to the perfect quality of the crystal surfaces. As-grown crystals were more effective for longer wavelengths than commercially available crystals into which a certain amount of imperfection presumably had been introduced.