Time Differences Between Friedel Reflections: Accuracy of Crystal Setting and Requirements on Beam Stability

In synchrotron radiation data collections where the wavelength is carefully set to optimize f''-derived crystallography intensity differences (Friedel pairs), careful alignment of the crystal is useful to minimize the time differences of stimulation of the reflections in the pairs. This paper quantifies these time differences as a function of crystal misorientation, with typical parameters, using the angular velocity of the crystal. Likewise, the time spent in the diffraction condition is also calculated via the angular reflecting range for a common synchrotron beam geometry. These times offer the user direct insight into the time-dependent aspects of the diffraction measurements. This therefore allows the optimum conditions to be set up so as to extract as accurate anomalous differences as possible in the context of synchrotron radiation beam stability and lifetime.