Executive SummaryThe Department of Energy Office of Nuclear Safeguards (NA-241) is supporting the project "Coincidence Counting With Boron-Based Alternative Neutron Detection Technology" at Pacific Northwest National Laboratory (PNNL) for development of an alternative neutron coincidence counter. The goal of this project is to design, build and demonstrate an alternative system based upon boron-lined proportional tubes in a configuration typical for 3 He-based coincidence counter applications.The specific application selected for boron-lined tube replacement in this project was one of the Uranium Neutron Coincidence Collar (UNCL) designs. This report, providing results for model development of a UNCL, is a deliverable under Task 2 of the project.The current UNCL instruments utilize 3 He tubes. As the first step in developing and optimizing a boron-lined proportional counter based version of the UNCL, models of eight different 3 Hebased UNCL detectors currently in use were developed and evaluated. Neutron-count efficiencies and corresponding die-away times from those eight modeled systems are reported, and compared to measurements for those systems with values reported in the literature. The reported experimental measurements for efficiencies and die-away times agree to within 10%.

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Executive SummaryThe Department of Energy Office of Nuclear Safeguards (NA-241) is supporting the project "Coincidence Counting With Boron-Based Alternative Neutron Detection Technology" at Pacific Northwest National Laboratory (PNNL) for the development of an alternative neutron coincidence counter. The goal of this project is to design, build and demonstrate a boron-lined proportional tube-based alternative system in the configuration of a coincidence counter. This report discusses the validation studies performed to establish the degree of accuracy of the computer modeling methods currently used to simulate the response of boron-lined tubes. This is the precursor to developing models for the uranium neutron coincidence collar under Task 2 of this project.The strategy for this project going forward is to use the model parameters that provide adequate comparison to experiment, which may or may not be related to the actual material or thickness of the lining. No information from the vendor on the actual boron coating was used in this study. A boron metal thickness of 0.75 µm appears to be an adequate value to use for models of boronlined tube systems based upon the current tubes supplied by General Electric Reuter-Stokes for testing. Good agreement between measurement and model was obtained for close geometries, though agreement was not as good at larger distances, where the models over predict response. This may indicate that the model of the room environment needs to be improved. This work will be extended over the next several months to more comparisons of models to experiments to improve the agreement that can be obtained. The results from this work will be applied to the development of the coincidence collar models using boron-lined tubes.

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