On the Calibration and Accuracy of the Guinier Camera for the Determination of Interplanar Spacings

Equations describing the relative mean error in the determination of interplanar spacings have been theoretically deduced for transmission cameras and X-ray investigations with and without internal standard. Together with standard film exposures of known substances these equations may be used to determine once and for all the accuracy of a Guinier camera under different experimental conditions. This is shown for an 80 mm camera positioned asymmetrically to the incident beam (α = 30 deg). Pieces of Scotch tape were used as powder sample holders, and comparator measurements on k (α1 + α2) spectra as well as rapid d-scale readings are discussed. It was found that a camera constant substantially independent of Θ can be determined most accurately for any film with the aid of only a few calibration lines diffracted to high Θ angles if for an optimal line measuring accuracy of ± 0. 01 mm the sample is never allowed to deviate by more than ± 0. 05 mm from the focussing cylinder defined by the film position. Using tape as sample holder, this condition can be fulfilled with a probability of at least 80 %. With thin glass slides on the other hand, the systematic error may be reduced so far that the use of internal standards after the primary calibration of a camera will appear unnecessary