THE BOX SEGMENTED NEUTRON SCANNER COMPONENT OF THE PROPOSED INTEGRATED BOX INTERROGATION SYSTEM, IBIS

Canberra Industries and LANL have collaborated in designing a next generation Integrated Box Interrogation System, IBIS, to meet the requirements of the solicitation INEEL/EXT-99-00121 for boxed waste Non Destructive Assay Development and Demonstration. IBIS comprises a standalone Box Segmented Gamma Scanner, BSGS, and a trailer-mounted Box Segmented Neutron Scanner, BSNS, integrated by software to generate, from the wealth of complementary data the two sub-systems produce, a single, justifiable, best estimate assay result. This paper describes the findings of the conceptual design study of a Box Segmented Neutron Scanner, BSNS. The BSNS described here is a combined high performance differential die-away chamber and passive neutron correlation counter of novel design. The BSNS design study concentrated on satisfying several aims: characterization and correction for matrix heterogeneity, characterization of source heterogeneity and isotopic composition, assay of high density matrices, correction for radioactive material physical form (e.g.self-shielding or multiplication), and calibration with a minimal set of reference standards and representative matrices. The counter design efforts entailed optimizing both the passive and the active responses of the chamber via extensive MCNP calculations. The hub of both the active neutron and passive neutron counting assays is the PATRM/PCI board, a newly developed dedicated nucleonics package. Much of the active and passive imaging capability depends on the analysis of the list mode data the PATRM/PCI unit provides. Further the imaging analysis is provided by newly developed software, based on the existing Combined Thermal- Epithermal Neutron (CTEN) differential die-away and Tomographic Gamma Scanning (TGS) (extended to neutron imaging) algorithms.