Experimental and simulation results for inherent unsharpness estimation of cassette contribution

In the absence of motion unsharpness, which can usually be neglected in industrial radiography, the total unsharpness is defined as the square root of the sum of the squared geometrical and inherent unsharpness. While the concept of geometrical unsharpness is well understood, and to a certain extent can be controlled by the radiographer with a careful consideration of the distance between the source, the object, and the film, inherent unsharpness is directly related to the radiation energy. Inherent unsharpness is produced by scattered secondary radiation within the cassette containing the photographic emulsion, which in turn renders silver halide grains within a certain vicinity of the primary radiation's absorption developable. This vicinity increases with the energy of the generated electrons, which in turn depends on the energy of the incident radiation. With digital radiography, it is relatively straightforward to determine inherent unsharpness. With film radiography, this is not the case. However, a detailed comparison of the values of this unsharpness between these two techniques is important for transitioning from one to the other, with implications for industrial implementation or regulatory requirements. This study presents the results obtained through simulation and experiments on measuring this unsharpness in film radiography using different methods, including the Klasens method, which involves evaluation of the profile of a particular edge image.