Determining distribution of chemical element in sample - by comparing X=ray transmission images for sample at wavelengths on each side of element absorption line

摘要

A parallel beam of monochromatic X-rays is passed through the sample and the transmission image produced is recorded, e.g. by a photosensitive plate or a scanning point detector. Images are produced at wavelengths above and below the X-ray absorption line for the element to be located. A comparison of the two images enables the distribution to be determined. The X-ray beam can be produced by a synchrotron, and a filter may be used or a monochromatic operating on the Bragg reflection principle. For large samples, the images can be recorded for several angles of incidence of the beam to enable depth distribution to be deduced. The technique is not limited by sample thickness, whereas existing non-destructive techniques are suitable only for samples of about 1 mu m. It is not necessary to operate under vacuum for wavelengths of 4 angstroms and biological samples can therefore be analysed.