Year
2008
Abstract
A Modified Hydrogen Correction (MHC) using the ratio of measured Triples and Doubles rates has been developed in an effort to reduce the impact of moderating materials on the coincident neutron response of the Box Neutron Assay System (BNAS). The MHC is an alternative and complementary technique to the Add- A-Source (AAS) matrix correction approach when the matrix is both severe and a sufficient quantity of Pu is present, and offers a reduction in bias for certain measurement conditions. The technique was inspired by the Los Alamos (LANL) Hydrogen Correction Factor1 developed previously but is different in form. This work summarizes our observations that led to the creation of the MHC. The BNAS is the neutron complement of the Integrated Crate Interrogation System (ICIS) developed for use at the Savannah River Site (SRS) to assay transuranic (TRU) waste. The BNAS was designed and calibrated to assay large containers up to and including the standard large box (SLB-2). The development of the MHC was based on the Cf-252 data acquired for the multi-position AAS calibration for the various container types. The data were evaluated in terms of Pu-mass ‘Recovery’, a concept used in evaluation of the Performance Demonstration Program (PDP) where ‘Recovery’ is the observed mass value divided by the expected mass value. Initially a form of the LANL hydrogen correction factor was evaluated using the calibration data on 200 drums. The evaluation showed that when the correction was applied there was significant structure to the corrected recovery. We conclude that this modified form of the hydrogen correction more accurately represents the observed response.