Masquerade: removing non-sample scattering from integrated reflection intensities

Abstract

X-ray diffraction experiments at very low temperatures require samples to be isolated from atmospheric conditions and held under vacuum. These conditions are usually maintained via the use of beryllium chambers, which also scatter X-rays, causing unwanted contamination of the sample's diffraction pattern. The removal of this contamination requires novel data-collection and processing procedures to be employed. Herein a new approach is described, which utilizes the differences in origin of scattering vectors from the sample and the beryllium to eliminate non-sample scattering. The program Masquerade has been written to remove contaminated regions of the diffraction data from the processing programs. Coupled with experiments at different detector distances, it allows for the acquisition of decontaminated data. Studies of several single crystals have shown that this approach increases data quality, highlighted by the improvement in internal agreement factor with the test case of cytidine presented herein. research papers J. Appl. Cryst. (2012). 45, 292-298 J. A. Coome et al. Masquerade 293 Figure 1Calculating the distance between the crystal and the shroud wall, n. The crystal position is at point A, the shroud wall is at point B, and the PIP of the Be reflection is at point C. S 1 is the vector from the crystal position to the PIP, with components S 1 ðxÞ, S 1 ðyÞ and S 1 ðzÞ. 2 Be is the angle between the direct beam and the vector from the PIP to the shroud wall.

HTD2: a single-crystal X-ray diffractometer for combined high-pressure/low-temperature experiments at laboratory scale

“…To reach the lowest possible temperatures by means of conduction cooling with a helium cryostat, two beryllium domes serving as vacuum and radiation shields have to be placed around the sample. Scattering of the primary beam by the texturized polycrystalline beryllium of the domes leads to a background with speckled Debye-Scherrer rings (Coome et al, 2012;McMonagle & Probert, 2019) [see Fig. 2(c)].…”

“…2(d)]. In contrast, beryllium metal as an alternative material generates stronger and more inhomogeneous background scattering than Kapton foil (Meserschmidt et al, 2003;Coome et al, 2012;McMonagle & Probert, 2019). However, it reflects thermal radiation more effectively and is robust enough to be manufactured into a thin and monolithic dome [inset in Fig.…”

Reducing the background of ultra-low-temperature X-ray diffraction data through new methods and advanced materials

“…In the case of weakly diffracting crystals, the irregularities in the background can be of the same order of magnitude as the sample reflection intensities, making the extraction of accurate observed reflection intensities difficult. Methods have previously been developed to improve this situation by collecting data at multiple detector distances in combination with a complex set of 'masks' during data reduction to ensure that the intensities from those reflections most affected by scattering from the shrouds are discarded (as implemented in the program Masquerade; Coome et al, 2012).…”

Structure of organic solids at low temperature and high pressure

“…Such a program is 'Masquerade' which uses the known position of the shrouds and the simulated diffraction pattern of beryllium to determine where 105 scattering from beryllium will occur on the overall diffraction pattern, and the appropriate corrections are made. 34 …”