Thickness testing using a new relationship between film density and penetrated thickness in radiography

To improve accuracy in thickness testing using radiography, a new relationship between film density and penetrated. thickness is proposed and experimental verification of the proposed relationship is carried out by using the X- and y-ray radiographs of two carbon steel step wedges. A new parameter, the logarithmic gradient of film density, was defined to express the characteristics of the radiographic film for a wider range of film density. A new relationship between the film density and the penetrated thickness was formulated using the logarithmic gradient of the film density. In the experiment, the logarithmic gradient of the film density was affected neither by the exposure nor by the film density. The logarithmic gradient of the radiographic film used in the present work was measured from the slope of the fitting lines in the plotting of logarithmic exposure versus logarithmic film density. Experimental results verified the accuracy of the proposed relationship between film density and penetrated thickness for the range of film density from 1.0 to 3.5. The thickness can be more accurately determined by using the proposed relationship and the parameters determined by our experiment. It is also found that the y-ray, having a simple energy spectrum, is a more appropriate radiation source for the testing of the thickness from the film density of the radiograph.