In this study, a standard test piece (termed a phantom) was designed to determine the minimum detectable refraction angle in X-ray diffraction-enhanced imaging (DEI). The phantom had an acrylic exterior and a pentagonal prism shape with a continuously variable angle α that corresponded to the supplementary angle of two X-ray irradiated planes. The refraction angle was affected by the inclination angle of the two irradiation planes when the X-rays were normally incident to the surface. Thus, the minimum detectable refraction angle was determined from the observed contrast. The boundary of the phantom between the slant face area and the flat plane area was clearly recognized for a large angle α. However, the boundary image was not observed for extremely small α values. In the latter case, the refraction angle for the X-ray beam was less than the angular resolution of the DEI equipment used. In the present study, the minimum detectable refraction angle for the DEI apparatus in the optical system constructed in a vertical-wiggler beamline (the BL-14B beamline) at the Japanese KEK-PF synchrotron facility was determined. The results indicated that the minimum detectable refraction angle was 3.8 × 10−6 rad for a 30 keV X-ray beam, as determined using an asymmetric 440 reflection collimator with a 10° off-angle and a symmetric 440 reflection analyzer.
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