A RADIOACTIVITY ASSAY-METHOD USING COMPUTED-TOMOGRAPHY

A nondestructive radioactivity assaying apparatus, especially suitable for miscellaneous waste drums, has been developed. The apparatus employs a simplified computed tomographic technique in the analytical process. The method uses 10 x 10 (horizontal) x 9 (vertical) density and radioactivity distribution information measured by NaI(Tl) detectors and an external source to compensate for photo-peak count rates from a germanium detector. Methods to compensate for the inhomogeneity of miscellaneous solid wastes are discussed. A detailed comparison of the proposed method with two other simplified methods, using >200 kinds of mockup wastes, showed an improvement in measurement precision for the proposed method over the conventional methods. The overall precision for measurements on the untreated miscellaneous waste was evaluated to be within 30 % when using the proposed method.