GB1414456A - Combination of photosensitive element suited for use in radiography - Google Patents

Abstract

1414456 X-ray intensifying screens AGFAGEVAERT 9 Nov 1971 [5 Nov 1971 31 May 1972] 50996/72 and 25529/72 Divided out of 1414455 Heading H5R [Also in Division G2] A light sensitive element (see Division G2) for radiographic use includes a support bearing on each side a light-sensitive silver halide emulsion layer each containing silver halide grains spectrally sensitized by means of one or more sensitizing dyes to light in the wavelength range 450-570 nm.; each layer being capable by exposure to such light and full development of a covering power of more than 50; and the emulsion layers together containing silver halide in an amount equivalent to less than 8 gm. of silver per square metre. For radiography, the element is combined with an X-ray fluorescent intensifying screen having more than half its spectral emission above 410 nm. and its maximum in the range 450-570 nm., and an intensification factor of at least 20 at 40 KV and at least 25 at 80 KV. The combination, by permitting the use of a minimum of silver halide per unit of surface, facilitates rapid processing. The intensifying screen may be separate from, or integral with, the photosensitive material, which may have the emulsion on one or both sides of the support. To reduce, in the latter case, the blurring effect of "cross-over", i.e. arising from the diffusion of light emitted from the screen in passing to the emulsion on the further side of the support, a "screening dye", absorbing the fluoresencent light by an amount which increases with the greater path length associated with increasing obliquity of the light path, is included in the fluorescent layer, or as a subjacent antihalation layer, or in both. Examples of suitable materials, which may include pigments such as carbon black, are listed. The effect of cross-over is further reduced by the inclusion of "filtering dyes", absorbing the fluorescent light, in the emulsion layers or their support; examples of suitable dyes are listed. Suitable fluorescent materials for the screen include rare earth oxysulphides and oxyhalides activated with other rare earths, of which examples are given, having a grain size in the range 1-25 micron, and dispersed in a binder, e.g. cellulose nitrate, ethylcellulose, cellulose acetate, polyvinyl acetate, polystyrene, polyvinylbutyral, polymethyl, and methacrylate. The material may form a sheet 0À05 to 0À5 mm. thick, which may be provided with a protective surface layer of cellulose nitrate, cellulose acetate, and polymethyl methacrylate.