X-ray topography of natural beryl using synchrotron and conventional sources

Abstract

Continuous-spectrum synchrotron-radiation Laue transmission topographs of natural beryl have been compared with the corresponding projection topographs taken with conventional apparatus and Cu Kα 1 and Mo Kα 1 radiations in an analysis of configurations of grown-in lattice defects and of the diffraction contrast they produce. The natural defects studied included grown-in dislocations, impurity zoning and fault surfaces. A growth-sector map was constructed for the (0001) specimen slice examined. Differences of contrast among the various reflections appearing on the synchrotron-radiation topographs are discussed and it is demonstrated that the contrast characteristics of the synchrotron-radiation images which consist of a superimposition of 3{\bar 2\bar 1}1 and 6{\bar 4 \bar 2}2 reflections can be satisfactorily synthesized by a weighted superimposition of the 3{\bar 21}1 image recorded with Cu Kα 1 and the 6{\bar 4\bar 2}2 with Mo Kα 1. Synchrotron-radiation damage to the crystal manifested itself on the X-ray topographs both as area contrast and as contrast at the periphery of the irradiated area, yet no visual absorption or birefringence due to this damage was detected. Annealing at 770 K for 3 h completely removed the contrast due to radiation damage.