Luminescent Screen and Intensifying Screens

The x-rays Photons making the image on radio-graphic film can not be seen from human eye. The information passing through is converted to image by following methods;

• A Photographic emulsion can be exposed to x-rays directly,
• The energy of x-rays is converted to visible energy spectrum, and that light may be used to expose the films or this light can be view directly.

Fluorescence:

Luminescence refers to the emission of light by a substance by any kind of stimuli for example light, chemical reaction, ionizing radiation etc. But Fluorescence is a kind of Luminescence when light is emitted instantaneously. Fluorescence is used in radiology because the fluorescent material mostly inorganic crystal has ability to emit light when it is exposed to x-rays. with such kind of materials image intensifying screen are fabricated. The main purpose of these are to reduce the x-ray dose to patient and get the maximum results and a best image. The x-ray films used in intensifying screen has photosensitive emulsion on both sides.

In early seventies, Calcium Tungstate was used as phosphor in most of the screens, later own new other phosphor were also used to make the film faster, there are three main methods to make a screen fast,

• Thicker phospher layer
• High conversion efficiency of the phospher
• High absorption Phosphers

CaWO4 screen speed is mostly measured by the thickness of the phosphers.