Iterative reconstruction and statistical optimization for the nondestructive assay of distributed gamma source in a large nuclear waste container

An iterative reconstruction and statistical optimization method for the nondestructive assay of total source activity of distributed gamma source in a large nuclear waste container is presented. Multiple detectors positioned as closely as possible to the waste barrel are used to measure the emerging radiation field from the distributed radiation source. The source distribution is reconstructed by using the conjugate gradient with nonnegative constraint method or maximum likelihood expectation method based on measured detector responses. Total source activity is estimated by examining the error bond and its associated confidence level. These are determined statistically by performing a large number of numerical experiments involving the counting statistics, the nonuniformity of source distribution, and the heterogeneous density of the self-absorbing medium. Using the conjugate gradient with nonnegative constraint method (CGNN) and maximum likelihood expectation maximum method (MLEM) methods the authors compare results of total activity estimation.