Recording of radiation

Abstract

When X-rays pass through matter they are absorbed to an extent which depends on the thickness and density of the material and on the wavelength of the radiation. The properties of differential attenuation and the essentially linear propagation of X-rays provide the fundamental bases of radiography. The presence of internal cavities and inhomogeneities in an object will produce local variations in the spatial intensity of the emergent beam of an initially homogeneous beam of X-rays, in other words, the emergent beam will contain an ‘image’ of the internal structure of the object. However, X-rays are not directly perceptible to the human senses and the information contained in the X-ray beam must be converted to some form which can be appreciated by eye. A detecting medium which will reveal this information by means of a secondary interaction of X-rays with matter is therefore necessary. Such a detecting medium may give an indication of the spatial variations in intensity over an area, i.e. a two-dimensional detector, or it may be necessary or desirable to obtain a point-by-point measure of radiation intensity by a scanning procedure.