IN a recent paper1 the present authors described a computer program which had been developed to index. Laue back reflection patterns of cubic crystals. The.
If the sought-for reflection is not already in the experimental set, then the "most probable" location (x*, y*) of a reflection with desired indices (hkl) may be determined by solving the two-dimensional minimization problem: z* = z(x*, y*) = Min z(x, y), x,y where the sum of squared errors,
[1]
n
z(x, y) = £ [Cos $>i(x, y) - Cos y, between the (hkl) reflection and the other axes, x and y of the specimen can be obtained by using the coordinates (, 0) and (0, °°) for x% and yt yielding: Cos 4>v =
[n]
and Cos
[12] VOLUME 2, AUGUST 1971-2295
The orientation of the crystal axes may be directly determined by locating the principal crystallographic directions, [100], [110] and [ill] in the film plane. The specimen itself may be reoriented to bring any desired plane normal to the x-ray beam. This is accomplished by rotating the specimen through an angle, a, around the beam moving the appropriate reflection to the #-axis. Here: « = tan-1 (g)
[13]
A second rotation through the angle, 4> s , around the y-axis brings the reflection into coincidence with the beam. In solving a typical pattern, the above scheme added less than 5 sec of computer time to the 15 sec required initially to index the reflections, thereby solving the pattern. Further details about these programs may be obtained from either J. H. Christensen or R. J. Block of the University of Oklahoma. 1. W. H. Huang, J. H. Christensen and R. J. Block,Met. Trans., 1971, vol. 2, pp. 1367-70. 2. R, Fletcher and C. M. Reeves: Computer J., 1964, vol. 7, p. 149.
