An adjustable curved crystal monochromator for X-ray diffraction analysis

The logarithmic spiral form of Barrau d’s monochromator can be obtained to a good approximation by exerting unequal bending moments on the short edges of a rectangular crystal plate. In the first two paragraphs some aberration formulas are derived pertaining to the asymetrical Barraud -type monochromator. In § 4 the new way of mounting is described. The aberration due to its approximative character is calculated. It appears to be negligible in the case of a monochromator, constructed and successfully used in this laboratory, the details of which are described in § 6. Finally it is an advantage of the device that there is no high precision work needed in making the crystal holder; further, that the monochromator can easily be set to a large range of wave lengths and crystal-to-focus distances.