• Human senses cannot perceive an X-ray and can be utilized only because it affects the emulsion of photographic film and produces fluorescence in certain crystals.

The photographic Effect

• X-ray affect photographic emulsion in almost the same way as do the photons of visible light. the emulsion consists of silver halide grains suspended in gelatin.

• When an X-ray or light photon hits a grain of silver halide a complex interchange of electrons takes place which liberate the halide atoms and leave metallic silver.

• The effect is still invisible and is referred to as the latent image. The film must be placed in a developer to complete the chemical reduction of the silver halide before the image is visible.

The Fluorescent Effect

• The fluorescent effect is used in diagnostic radiography in two main ways: As intensifying screens. calcium tungstate crystals which fluoresce blue, a color to which photographic emulsion is most sensitive, are coated on cards and "sandwich" the film in light-tight film holder, called a cassette. Thus light is used as well as the x-ray beam to affect the film emulsion.

• Direct fluoroscopy or screening. The screen employed for fluoroscopy use zinc sulphide which fluoresces green, the color to which the eye is most sensitive. It is used in darkened room to visualize the structure of the patient and to observe their movements.

The Biological Effect of X-rays

• The effect of the absorption upon the cells of the body is complicated and still not fully understood. The ionizing of the atoms and consequent disturbance to the chemistry of the cell can be lethal after a sufficiently large dose of  X-rays.