Experiments on the Variation of the Atomic Structure Factor of Potassium with X-Ray Wave-Length

A vacuum ionization spectrometer has been constructed in which an externally controlled, motor-driven slide brings either of two powder specimens into the path of the primary x-ray beam. Comparison of the diffracted power in the Debye-Scherrer rings from NaCl, NaF, LiF, and KF powders have been made, with a FP 54 Pliotron circuit to detect the ionization currents. In the studies on KF a range of wave-lengths from 1.538A to 4.146A has been used. On the short wave-length side, the expected decrease of the crystal structure factor was observed in KF. Beyond the K edge of potassium, the crystal structure factor rose again, but considerably more than predicted. Conclusions: H\"onl's computations based on the wave-mechanical theory of x-ray dispersion do not correctly give the observed structure factor differences for the (200) diffraction halo from powdered potassium fluoride on the long and short wave-length sides of the potassium K edge. The predicted invariance of the structure factor decrement due to K electrons with scattering angle for light elements is confirmed in our experiments.