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Computed Tomography (CT) using X-ray attenuation by atomic effects is now widely used for medical diagnosis and industrial non-destructive inspection. In this study, we performed a tomographic imaging of isotope (208Pb) distribution by the Nuclear Resonance Fluorescence (NRF), i.e. isotope specific resonant absorption and scattering of gamma rays, using Laser Compton Scattering (LCS) gamma rays. The NRF-CT image which includes both effects of atomic attenuation and nuclear resonant attenuation was obtained. By accounting for the atomic attenuation measured by a conventional method at the same time, a clear 208Pb isotope CT image was obtained. The contrast degradation due to notch refilling caused by small-angle Compton scattering is discussed. This study clearly demonstrates the capability of the isotope-specific CT imaging based on nuclear resonant attenuation which will be a realistic technique when the next generation of extremely intense LCS gamma-ray sources will be available. The expected image acquisition time using these intense LCS gamma rays was discussed.

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The isotope selectivity of computed tomography (CT) imaging based on nuclear resonance fluorescence (NRF) transmission method using a quasi-monochromatic laser Compton scattering (LCS) gamma-ray beam in the MeV region was demonstrated at the Ultra Violet Synchrotron Orbital Radiation-III (UVSOR-III) Synchrotron Radiation Facility (Institute of Molecular Science, National Institute of Natural Science) for two enriched lead isotope rods (206 Pb and 208 Pb) implanted in an aluminum cylinder. Since these two rods show the same gamma-ray attenuation in atomic processes, it is impossible to differentiate between them using a standard Gamma-CT technique based on atomic attenuation of gamma rays. The LCS gamma-ray beam had a maximum energy of 5.528 MeV and an intensity of approximately 5.5 photons/s/eV at the resonance energy (J π = 1 − at 5.512 MeV in 208 Pb). A lead collimator with a hole diameter of 1 mm was used to define the size of the LCS gamma-ray beam at the CT target. The CT image of the 208 Pb rod was selectively obtained with a 2-mm pixel size resolution, which was determined by the horizontal step size of the CT stage. Index Terms-Computed tomography (CT), isotope distribution, laser Compton scattering (LCS) gamma-ray beam, nuclear resonance fluorescence (NRF). I. INTRODUCTION N ONDESTRUCTIVE assay (NDA) technology, which is used to identify specific isotopes in a substance,