The Neutron radiography facility (NRF) at Oregon State University (OSU) has been modified to begin working on the non-destructive evaluation of concrete materials to study the early stages of shrinkage, cracking, and water transport of concrete during the curing process.
The objective of this work is to investigate the efficiency and spatial resolution of the NDDL 40 Micro-channel plate (MCP) detector for the use of neutron radiography and tomography with the eventual goal of concrete imaging. Working in collaboration with the School of Civil and Construction Engineering, the NRF at OSU has added a NDDL 40 vacuum sealed neutron imaging detector with a delay line system readout developed by Nova Scientific Inc. The detector provides leading technology that grants high detector efficiency and high theoretical spatial resolution of ~50 µm which is the major metric for generating both 2D and 3D images. Using the patented technology, the detector uses borated micro-channel plates to convert incoming thermal neutrons through the ¹⁰B(n,α)⁷Li process. This converts the neutron into an α and lithium ion, which through secondary interaction create an electron avalanche and is amplified to a signal that can be detected.
The NDDL 40 MCP detector has been shown to be capable of producing radiographs and tomography. Through tedious procedures radiographs continually had inconsistent results in image quality due to the dynamic background, signal to noise ratio and dramatically decreased detector efficiency. This led to issues in the rendered tomographic models. Through the extensive measurements and the use of ASTM standards the NDDL-40 MCP detector was determined to have an optimum efficiency of 6% with a maximum spatial resolution of 50 to 200 µm.
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