HIGHLIGHTS IN THE HISTORY OF X-RAY TOPOGRAPHY

X-ray topography provides a non-destructive method of mapping point-by -point variations in orientation and reflecting power within crystals. The discovery, made by several workers independently, that in nearly perfect crystals it was possible to detect individual dislocations by X-ray diffraction contrast started an epoch of rapid exploitation of X -ray topography as a new, general method for assessing crystal perfect ion. Another discovery, that of X-ray Pendellosung, led to important t heoretical developments in X-ray diffraction theory and to a new and p recise method for measuring structure factors on an absolute scale. Ot her highlights picked out for mention are studies of Frank-Read disloc ation sources, the discovery of long dislocation helices and lines of coaxial dislocation loops in aluminium, of internal magnetic domain st ructures in Fe-3 wt.% Si, and of stacking faults in silicon and natura l diamonds.