Photographic Aspects of the Definition Attainable in Radiographs

Paper to be presented at R.P.S. Symposium on “Photographic Aspeels of Ionizing Radiations”, organized by the Scientific and Technical Group on 15–17 April 1964, at Oxford.

Abstract

The definition attainable on a radiograph is canveniently measured in terms of the “unsharpness” of the image of a physically sharp edge. There are four main causes of radiographic unsharpness—geometric, movement, intensifying screens, and film—but in industrial radiogrophy only geometric and film unsharpness are significant, except when salt intensifying screens are used. With X-rays of energy up to 200 kV the film unsharpness of non-screen X-ray film is c. 0-Imm and geometric unsharpness is usually predominant. With high-energy X-rays however (above I MV) the film unsharpness has been measured to be fram 02-O8mm and becomes the dominant factor. Methods of measuring this film unsharpness are described and its significance in limiting the sensitivity attainable in radiography is discussed. The magnitude of film unsharpness can be predicted from a knowledge of electron ranges in film emulsions and a possible relationship between film unsharpness, graininess and the number of X-ray quanta adsorbed during an exposure, is discussed. An attempt has been made to relate radiographic unsharpness and resolving power of films and it seems probable that recent work on frequency response curves can also be related. The experimental difficulties in making frequency response curves with high-energy X-rays are discussed.

Notes

Paper to be presented at R.P.S. Symposium on “Photographic Aspeels of Ionizing Radiations”, organized by the Scientific and Technical Group on 15–17 April 1964, at Oxford.