An x-ray sensitometer is used to measure the characteristic curve of r
adiographic films exposed with fluorescent intensifying screens. The s
eries of relative exposures, necessary to cover the full density range
of the film, can be obtained by either time-scale or intensity-scale
sensitometric methods. We have developed a convenient method of exposi
ng film-screen systems for time-scale sensitometry. In this method, du
ring exposure the x-ray kilovoltage, tube current and x-ray intensity
remain constant and a geometric series of exposures of the film is mod
ulated by varying the exposure time. This time variation can be obtain
ed when a lead disc with different sector openings is rotated in front
of the film system by a stepping motor. The conditions normally used
are 70 kVp x-rays, 3.5 mm Al total filtration at the tube, and 2.4 m f
ocal spot-film distance. This exposure latitude gives a complete chara
cteristic curve of film-screen systems.