Measurement of absorption curves for protein single crystals on the oscillation camera with time decaying incident-beam intensity and variable-wavelength synchrotron X-radiation

The correction of intensity data from protein single crystals for sample absorption effects is important for refinement and interpretation of atomic parameters. Synchrotron X-radiation sources are extensively used to provide high-resolution data and their tuneability utilized to collect data with optimized anomalous dispersion. At longer wavelengths the sample absorption effects become increasingly important. Previous methods of determining the absorption correction using the oscillation camera relied upon film methods, which cannot readily take account of the decay in incident-beam intensity of synchrotron sources. The use of a sensitive ion chamber to measure the transmitted intensity and monitoring of the incident intensity allows an empirical absorption correction to be calculated directly.