This invention relates to the use of thick target materials 50 microns and thicker for an x-ray transmission tube; to possible target material compositions including various elements and their alloys, eutectic alloys, compounds, or intermetallic compounds; and applications for utilizing such thick target transmission x-ray tubes. The target comprises at lease one portion of the target with a thickness of 50 microns or greater. The target can be optionally attached to a substrate end-window essentially transparent to x-rays or be thick enough so that no such substrate is required. Applications include producing a high percentage of monochromatic line mission x-rays of said thick target for use in reduced dose medical imaging and other non-destructive testing applications.