X-ray determination of the thickness of thin metal foils

The interpretation of neutron cross section experiments depends upon an in-depth knowledge of the physical characteristics of the target sample. An x-ray image of an encapsulated metallic Eu sample used in a neutron cross section measurement showed a very non-uniform thickness as well as holes in the sample. In light of this problem it was found necessary to determine the thickness distribution in four thin metallic Eu samples without disturbing the encapsulation (and exposing the Eu to air). All four Eu samples were subsequently x-rayed along with a Sm step wedge. The gray levels in the Eu images were then compared to the Sm gray levels and, taking into account differences in the x-ray absorption and density of Eu and Sm, the sample thickness distributions were obtained for each Eu sample. This work demonstrates that a step wedge can be used to calibrate x-ray images to a thickness scale, and allows the thickness variation of the samples to be represented in a simple probability table for incorporation into the analysis of neutron experiments.