Abstract
One of the most noteworthy aspects of computed tomography (CT) based on the nuclear resonance fluorescence (NRF) transmission method is the isotope selectivity that makes it possible to discern an isotope of interest from other isotopes within a sample. We experimentally obtained a three-dimensional (3D) isotope-selective CT image based on the NRF transmission method (3D NRF-CT) for the enriched lead isotope distribution of 208Pb in a cylindrical holder in a previous study. The cylindrical holder’s diameter and height are 25 mm and 20 mm, respectively. The NRF-CT imaging technique requires a considerable data accumulation time. It took 48 h to obtain an image with a resolution of 4 mm/pixel in the horizontal plane and 8 mm/pixel in the vertical plane using a laser Compton scattering (LCS) gamma-ray beam with a beam size of 2 mm and a flux density of 10 photons/s/eV. Improving the NRF-CT image resolution with the existing hardware is challenging. Therefore, we proposed an alternative method to improve the NRF-CT image resolution using the fusion visualization (FV) technique by combining the NRF-CT image including isotopic information with a gamma-CT image, which provides better pixel resolution. The 3D gamma-CT image for the same sample was measured at the same beamline BL1U in the ultraviolet synchrotron orbital radiation-III (UVSOR-III) synchrotron radiation facility at the Institute of Molecular Science at the National Institutes of Natural Sciences in Japan under similar experimental conditions except for the LCS gamma-ray beam flux and beam size. Obtaining a 3D gamma-CT image with a resolution of 1 mm/pixel took 5 h using an LCS gamma-ray beam with a beam size of 1 mm and a flux density of 0.7 photons/s/eV. The data processing of the FV technique has been developed, and the 3D NRF-CT image quality was improved.
Highlights
Nuclear safeguards have a critical role in the non-proliferation of nuclear materials for reprocessing nuclear fuels and the control of nuclear materials
The procedures of the 2D gamma-computed tomography (CT) images calculation are detailed in references [13,14,21]
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Summary
Nuclear safeguards have a critical role in the non-proliferation of nuclear materials for reprocessing nuclear fuels and the control of nuclear materials. To improve the image resolution while keeping a reasonable data acquisition time, upgrading the detection efficiency of the NRF measurement system and/or increasing the gamma-ray beam intensity are possible approaches. One of the sources is the primary 3D NRF-CT image [14], which supplies the desired isotope distribution, but its image quality needs improvement Another data source is a high-resolution gamma-CT image for the same CT sample under similar experimental conditions measured at the beamline BL1U in the UVSOR-III facility but with some alterations in the LCS gamma-ray beam parameters. We describe the numerical treatment procedures of the FV technique for integrating the primary images of the 3D NRF-CT and the 3D gamma-CT to improve the quality of an isotope-selective 3D NRF-CT image. This article incorporates sub-elementary Materials (Movie S1 and Movie S2)
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