W0436

Analysis of the Diffraction Geometry using Multi-chromatic Beam Line. M. Allaire, National Synchrotron Light Source, Brookhaven National Laboratory, Upton, NY.

It is generally accepted that increasing the redundancy of measurements can enhance the quality of the diffraction dataset. With synchrotron radiation, we can build beam lines that deliver more then one single monochromatic wavelength. These multi-chromatic beam lines provide an opportunity to collect simultaneously multiple dataset at different wavelengths. Assuming minimum radiation decay from the crystals, these beam lines could represent an interesting way to increase the redundancy of the diffraction data. In order to succeed, the diffraction spots collected on the detector would need to be separated at these different wavelengths.

This paper presents the analysis of the diffraction geometry of a single crystal at different wavelengths. The analysis is done in comparing the Ewald sphere as a function of wavelengths. It is found that the separation of the spots on the detector can be evaluated from the known distance of the detector and the difference in the Bragg angles of the reflection at different wavelengths. Non-obvious, the analysis also reveals that the condition of diffraction at two wavelengths will occur at different rotation angle and is a function of the chi angle of the reflection.

This analysis, complemented by simulated data, revealed that it would be difficult to resolve spots from a MAD experiment if the inflexion point and the peak of the white line were to be collected simultaneously. On the other hand, if the two wavelengths differ enough, the analysis suggests that the multi-chromatic beam lines could represent a good tool to collect multiple dataset simultaneously. This would increase the redundancy of measurements and improve the quality of the data. These multi-chromatic beam lines could also be important in providing multiple measurements of the anomalous difference, e.g. for sulfur, at different wavelengths.