Showing papers by "Ulrich Geppert published in 1993"

Analysis of rocking curve measurements of LiF flight crystals for the objective crystal spectrometer on SPECTRUM-X-GAMMA

Abstract: The Objective Crystal Spectrometer (OXS) on the SPECTRUM—X—GAMMA satellite will usethree types of natural crystals LiF(220), Si(111), RAP(OO1), and a multilayer structure providinghigh-resolution X-ray spectroscopy of Fe, 5, 0, and C line regions of bright cosmic X-ray sources. 330 — 360 LiF(220) crystals of dimensions 23 x 63 mm2 are required to cover one side of a large(1000 x 600 mm2) panel, which is to be mounted in front of one of two high throughput X-ray tele- scopes. Rocking curves of 441 LiF(220) crystals measured by using an expanded Cu — Kc2 beam were analysed to select the best ones for the flight model. An important parameter is the non-parallelityof the crystal lattice planes with respect to the rear side of the crystals, since it is of the same orderof magnitude as the rocking curve width. By lapping the rear side to diminish the non-parallelityand selection the main parameters of the rocking curve averaged over all crystals can be improvedat least by a factor of 1.6 both in full width half maximum and peak reflectivity. Additionally, thetemperature dependence of the rocking curves was measured and turned out to be negligible if tem-perature variations stay within 3°C. Some first measurements were performed with an Fe —