Probabilistic interpretation of non-destructive assay of nuclear materials

The response of a non-destructive assay system for radioactive-waste containers depends on the spatial distribution of the assayed nuclear materials in the measured container. Therefore, interpretation of measured activity in terms of contained mass will be ambiguous unless the spatial distribution is specified. A probabilistic approach is presented by which the measured activity can be interpreted in terms of a probability distribution of the contained mass. A computationally feasible procedure is formulated for calculating the conditional probability of having a certain mass given a measured value of the activity. The procedure assumes random loading of the assayed material within the container, and accounts for variation of the mass, number and position of assayed items. The procedure is generalized to account for measurement of more than one radiation. A simple explanatory example is discussed. (author)