The Relative Intensities of Reflection of X-Rays from the Principal Atomic Planes of Fluorite

For these measurements, the usual Bragg apparatus was modified by adding a reference crystal illuminated through the same slit on a line slightly above the other, and a second ionization chamber and Bumstead electroscope. The integrated ionization as the crystal was turned by motor through a given line or range of wave-length was measured. Correction was made for the general radiation. Thus the relative intensities of the Pd $\alpha$ and $\beta$ lines when reflected from three principal planes of fluorite were determined. The values fall into three groups for each line, each of which fall on a smooth curve when plotted as a function of the angle of reflection, the strongest group being due to Ca and F atoms acting together, a weaker group to Ca atoms alone, and the weakest group to Ca and F planes which are out of phase with each other. Simple quantitative relations between the intensities of these groups have not yet been found, evidently because an additional absorption by the crystal takes place, which varies in an unknown manner with the angle of reflection.