Vol.8 No.2 2015

Research paper : Application of laser Compton photon beam to nondestructive tests (H. TOYOKAWA)−93−Synthesiology - English edition Vol.8 No.2 (2015) accelerator system that could be operated by one person, so that users could tune the LCS photon energy and intensity online.The image quality improved, and the CT image of spatial resolution of 1 mm or less was obtained.[8] We also obtained highly precise CT images (Fig. 6).[9] The CT numbers were accurately measured for various substances, and they were proportional to the linear attenuation coefficients in a wide dynamic range. We succeeded in achieving density resolution of 1 % or less (Fig. 7).[10] We were able to demonstrate its effectiveness as a measurement technology for infrastructure diagnosis such as for cracks of 0.2 mm width in concrete and CT of cross sections of reinforced steel concrete with 50 cm thickness.[11] Figure 8 shows how the elements are integrated to make a system.(3) Verification of the research resultsAs the automation of the device progressed, it became possible for the users themselves to conduct adjustment operation of the accelerator and to generate the LCS photon beam. This started to produce results in the CT research for open use. Joint research was conducted with companies and universities for many years. In this period, evaluations and improvements of the spatial and density resolutions were conducted, and we were able to achieve the performance that was initially set as our goal. The users gradually voiced requests for the development of small devices that can be installed in their own factories. To accomplish this, downsizing and cost reduction of the accelerator are mandatory.We need an electron storage ring or a continuous-beam electron accelerator of a few hundred MeV for the present method. Downsizing the CT system is almost equivalent to downsizing the electron accelerator. However, since the accelerator energy is proportional to the system size, it is difficult simply to decrease the size of each device. More development is needed such as the development of materials and a surface treatment technology that can resist high electric fields of several 100 MV/m or more; a machining technology of nanometer precision and technology; a Fig. 5 Transmission radiography using LCS photonsLeft: Stainless bolts were photographed using 10 MeV LCS photons (black-white are reversed). Right: Electrode part of high-frequency oscillator tube was photographed using 10 MeV LCS photons (spatial resolution 1 mm; part of the diagram was cited from Reference [8]). 100 mm x 70 mmSpatial resolution 1 mmFinal image10 cmhigh-frequency oscillator tube170 MHzInitial imageSpatial resolution 10 mm~Fig. 6 (Left) Sample photograph, (center) sinogram, and (right) CT image[9]The samples include water in a beaker and rods of various metals such as silicon, aluminum, and tungsten. Blue to green represent the low density ranges, while yellow to red show the high density ranges.Reconstructed image f(x,z)Actual image f(x,z)Sinogram g(X, θ)


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