New and hitherto unavailable data will be collected with many different x- ray monochromator crystals under identical conditions using a molybdenum target x-ray tube as primary source of divergent, unpolarized, 50 to 60 KEV polychromatic x-rays. From initial theta/ two-theta diffractometer scans, those crystals which exhibit high intensity higher order reflections will be selected for further studies including multichannel analyser deter- minations of multiple energy content of each of the reflections, rocking curve measurements for determination and comparison of acceptance angles, and "apparent performance" differences occasioned by the characteristics of at least two different detectors. Illustrations will be given of how these new data can be combined to design effective and efficient dual energy systems for potential application in such areas as mammography, medical CT, digital AND BONE DENSITY scanning and other diagnostic or NDT equipment design and development. Special aspects of this project are to establish an experimental basis for extending these measurements and techniques into the high KEV range of greater medical interest AND TO INITIATE PREPARATION OF A MONOGRAPH.