A New Fluorescent Screen for Visual Examinations

Abstract

Comparatively few substances have been employed in the construction of fluorescent screens for visual examination. The platinocyanides were the first substances to find practical application for this purpose, both the barium and potassium salts being originally employed. Barium platinocyanide, however, soon proved its superiority over the corresponding potassium compound, and until about 1912 this salt was the only substance employed in the manufacture of visual fluorescent screens. Although fluorescent screens made from barium platinocyanide are of high quality, the considerable cost of this salt and the fact that the screens deteriorated in use, led to a search for other substances which should be free from these objections. A detailed account of barium platinocyanide screens has been given in a previous communication by one of the authors.1 Synthetically prepared Willemite (zinc silicate) was the next substance to be employed for the construction of fluorescent screens, but screens made from this substance have never achieved any large measure of success for reasons which are discussed later on. The next development consisted in the use of cadmium tungstate, of which material practically all modern fluorescent screens are made and which has held the field almost exclusively since the war. The intensity of the illumination of a fluorescent screen when excited by X rays should be as great as possible for a given energy input to the tube.