The polarization ratio of crystal monochromators

A tabulation of some 40 measured values of the polarization ratio K (a measure of the fractional polarization introduced into an X-ray beam by a crystal monochromator) is presented. The values may be represented through the parameter n given by K = cos n2 theta sub M. The measured values of n cluster around unity and the theoretical rationale for this result is discussed. Possible explanations of outlying values are considered. It is recommended that the polarization ratio of an apparatus be measured using a direct method whenever possible, but methods for estimating a value of K are also given.