Measurement of the Mean and Anomalous Absorption Coefficients with the Three‐Crystal X‐Ray Spectrometer

Abstract

AbstractThe anomalous absorption coefficient 1/2 (σ1 — σ2) and the mean absorption coefficient σm are measured for the (220) and (111) reflections of Si single crystals for CuK radiation. The measured variation of the intensity of the diffracted beam with crystal‐thickness is composed of two exponential terms, one of which corresponds to strong absorption and the other to weak absorption of the wave field. The measurements are made with a three‐crystal X‐ray spectrometer which allows the relative angular position of the crystal under investigation to be controlled to within ±1″. The anomalous absorption coefficient is measured for the angle βr corresponding to equal to zero, values of 122 cm−1, and 75 cm−1 being obtained for the (220), and (111), reflections respectively. These values are smaller than those predicted theoretically due to the presence of imperfections in the crystals. The values of σm are 164 cm−1 and 154 cm−1 for the (220), and (111), reflections respectively, which agree with the theoretical values within the limits of experimental error.