The Iso-Pacific S3 utilizes a 72" wide sorter belt, which can accommodate a layer up to six inches in depth. The material is conveyed below the detector array in a thin layer whose depth and density is matched to the photon emission and attenuation characteristics of the contaminant of concern. There are no 'guess-timates' of attenuated subgrade activity that cannot be seen as with in-situ walkover scanning surveys.