Date of Award

8-2019

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Environmental Engineering and Earth Sciences

Committee Member

Timothy DeVol, Committee Chair

Committee Member

Jay Gaillard

Committee Member

Steven Serkiz

Committee Member

Lindsay Shuller-Nickles

Abstract

This work investigated a neutron detection media comprising porous nanomaterial membranes to mitigate self-absorbance of neutron reaction products (α, 7Li) typical of micron-sized neutron conversion layers. Porous 3D layers fashioned from boron nitride nanotubes were suspended in parallel-plate and anode-wire chamber configurations to test their viability as effective conversion materials. It was hypothesized that this design further mitigated wall-effect issues (i.e. loss of one of the neutron reaction products) that create poorly defined energy peaks and lower neutron detection efficiency of boron-lined proportional counters. Parallel-plate electrostatic modeling of the proposed detector was performed using COMSOL Multiphysics® with additional particle tracking predictions using SRIM/TRIM model computations. This work included neutron sensitivity evaluation, pulse shaping considerations, mitigation of adverse charging effects, gamma discrimination testing, and theoretical comparison to typical helium-3 and boron-10 detectors. It was systematically deduced that both reaction particles (α, 7Li) were found to be successfully detected from the porous boron nanomaterials suspended in a single-anode detector. Although not well understood, undesirable charging effects were mitigated by mixing CNTs with BNNTs. Neutron detectors utilizing boron nitride nanotubes (BNNT) assembled into 3D architectures have the potential to rival helium-3 detectors and boron gas-filled detectors by increasing the functional boron-10 number density, fill-gas ionization potential, and overall neutron sensitivity.

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