Neutron detection is important in several fields, especially detection of illicit nuclear material. Historically, 3He has been the basis for these technologies. Modern realities have necessitated the development of new technologies and the exploration of new materials to meet this need. One potential solution is known as capture-gating, which is a measurement approach that is good at differentiating between incident neutrons and gamma rays. The key issue is that materials used in current capture-gating devices can suffer from poor optical performance. This is due to the fact that the these detectors, whether composed of a heterogeneous or homogeneous mixture of materials, are made of dissimilar materials. In the homogeneous case, this frequently results in a cloudy material (e.g. lithium-gadolinium-borate crystals), while heterogeneous cases suffer from index mismatch (e.g. glass inside a plastic scintillator). The goal of this thesis is material development and processing toward an index-matched, gadolinium-based glass, heterogeneous capture-gated neutron detector. This involved identifying the refractive index range of known gadolinium glasses and the development of polystyrene (PS) and polyvinyl toluene (PVT) co-polymers with a range of refractive indices. Specifically 1:3, 1:1, and 3:1 PS:PVT ratios were manufactured and their refractive indices were compared to those of pure PS and PVT. Two methods for uniform glass dispersion were explored; the use of a rotisserie oven and the use of centrifugal planetary mixer. Ellipsometry, refractometry, and spectroscopic transmission were all performed to optically evaluate the manufactured polymers and polymer/glass composites. The ability to produce a PS/PVT copolymer with a refractive index in the range of known gadolinium glasses was demonstrated. In addition, the benefit of matching the refractive indices when producing a glass/polymer composite was explored and the effect of index mismatch was observed. The ability to predict the refractive index of a PS/PVT blend was demonstrated but can still be improved upon. While a novel index-matched gadolinium-based heterogeneous capture-gated neutron detector was not developed as part of this work, progress was made on all material aspects to further develop a detector meeting that description. More work still needs to be done in fine tuning the index match of the glass and polymer components, in determining the ideal method of glass dispersion, and in producing larger samples.



College and Department

Mechanical Engineering



Date Submitted


Document Type





capture-gated, neutron detection, gadolinium, polystyrene, polyvinyl toluene, index of refraction matching, copolymer, polymerization



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Engineering Commons