Graded SiGe crystals as X-ray collimators

Many X-ray applications could benefit from a beam conditioner providing a parallel beam with a small cross-section. The limiting values may vary with an application, however, not a single commonly used X-ray optical device is able to achieve these two requirements simultaneously without a drastic loss of the primary beam intensity. st promising way to overcome this limitation is using crystals with a gradient of the lattice parameter. Recent technological successes in growing high-perfection crystals of Ge–Si solid solutions [A. Erko, F. Schäfers, W. Gudat, N.V. Abrosimov, S.N. Rossolenko, V. Alex, W. Schröder. Nucl. Instr. Meth. Phys. Res. A 374 (1996) 408] make this goal achievable. The high quality of these crystals is experimentally confirmed [S. Keitel, C. Malgrange, T. Niemueller, J.R. Schneider. Acta Crystallogr. A 55 (1999) 855]. tudy shows that the gradient crystals allow making high-quality beam collimators overcoming the flux gain restrictions imposed by the flat or curved single crystals. Several types of collimators both for divergent and convergent beams are suggested.