Development of a practical conversion factor for evaluating radioactivity in mixed metal and plastic clearance objects

In clearance measurements involving a single material type, a conversion factor was applied to convert measurement results to activity based on an assumed uniform density. However, this factor has been found to underestimate activity in material mixtures. In this study, we proposed a method to identify the location with the lowest detection sensitivity (minimum location) in a mixture and evaluated its applicability to the conversion factor. We calculated this minimum location by determining the weighted average of a two-dimensional distribution of line attenuation coefficients, obtained through X-ray computed tomography (X-ray CT). We were able to identify the angle in polar coordinates using the center of the image as the origin, but the distance remained indeterminate. However, with this method, the minimum location can be identified along any straight line passing through the center of the image. This method has the potential to enhance activity evaluation for mixtures in cases where conservative evaluation of activity was previously unfeasible.