Journal of Applied Crystallography

Volume 35, Part 3 (June 2002)

research papers

J. Appl. Cryst. (2002). 35, 356-359 [ doi:10.1107/S0021889802005770 ]

The correction of reflection intensities for incomplete absorption of high-energy X-rays in the CCD phosphor

G. Wu, B. L. Rodrigues and P. Coppens

Abstract: It is shown that incomplete absorption of the X-ray beam in the phosphor of an area detector causes an incident-angle dependence of the recorded X-ray intensities. An energy scan of a SMART-6000 CCD (charge-coupled device) phosphor using synchrotron radiation shows the correction to be of importance above about 17 keV. Intensities of single reflections, each collected several times at different angles of incidence on the phosphor surface, show a pronounced angle-dependence at shorter wavelengths. Both conventional structural refinement and multipole charge density studies confirm that an oblique-incidence correction leads to improved quality of the results. Atomic displacement parameters will be systematically biased when the correction is not applied. For a [lambda] = 0.394 Å data set, neglecting the correction gives rise to artifacts in the deformation density maps that are likely to lead to misinterpretation of the experimental results.

Keywords: area detector; CCD phosphor; high-energy synchrotron radiation; oblique correction.