Selective Isotope CT Imaging Based on Nuclear Resonance Fluorescence Transmission Method

Abstract

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,

Fusion Visualization Technique to Improve a Three-Dimensional Isotope-Selective CT Image Based on Nuclear Resonance Fluorescence with a Gamma-CT Image

“…We operated the laser system at a typical average power of 2.4 W during measurement of the gamma-CT images to generate an LCS gamma-ray beam with an intensity of 7 × 10 6 photons/s with 100% energy bandwidth at the full width at half maximum (FWHM) before collimation. The EGS5 Monte Carlo simulation code [19] was used to estimate the LCS gamma-ray beam's properties after the collimation [13]. The estimated flux of the LCS gamma-ray beam after collimation was 0.7 photons/s/eV at a maximum energy of 5528 MeV with 1.1% energy bandwidth at the FWHM.…”

“…The LCS gamma-ray beam flux passing through the collimator was numerically estimated using the EGS5 Monte Carlo simulation code [19], and thus we found that the flux density was 10 photons/s/eV and that the maximum energy was 5528 MeV with 2.9% energy bandwidth at the FWHM, which was able to excite the J π = 1 − NRF level at 5512 MeV in 208 Pb. Although the NRF-CT imaging technique is time-consuming, we were able to shorten the image acquisition time for each measurement point, which had been measured in our previous research [13] by adjusting the CT sample scanning pattern and increasing the LCS gamma-ray beam's intensity flux. The overall time needed to obtain a 3D NRF-CT image was approximately 48 h. Reference [14] gives more details on the experimental setup, the CT sample scanning plan, and a schematic diagram of the 3D NRF-CT image.…”

“…Therefore, one can obtain a gamma-CT image for a sample using the gamma-ray transmission factor measurements of the off-resonance energy, known as off-resonance (ε off ) attenuation, which originates from the atomic effect. The procedures of the 2D gamma-CT images calculation are detailed in references [13,14,21]. Since the height of the CT sample holder was 20 mm, we divided it into 20 layers and added two extra layers; one of the two extra layers was located below the bottom of the CT sample and the other above it.…”

“…In our previous study [13], we obtained a 2D isotope-selective CT image based on the NRF transmission method for the distribution of an enriched lead isotope ( 208 Pb) and of another enriched lead isotope ( 206 Pb) implied inside an aluminum cylinder holder. The 2D NRF-CT image had a resolution of 2 mm/pixel with a data acquisition time of 60 h [13]. As a result, 208 Pb and 206 Pb were clearly distinguished.…”

Three-Dimensional Nondestructive Isotope-Selective Tomographic Imaging of 208Pb Distribution via Nuclear Resonance Fluorescence

“…The use of the nuclear resonance fluorescence (NRF) in combination with computed tomography (CT) has been demonstrated as an isotope imaging technique, allowing for nondestructive inspection (NDI) for detecting hidden isotopic compositions of target materials that are of interest [1]. Furthermore, the isotope selectivity assessment [2] is a significant advancement in nuclear engineering. Physically, NRF is a nuclear process in which a nuclear state is excited through the absorption of a photon whose energy is nearly identical to the excited energy of the nuclear state.…”