OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 24 No. 4 2022 The principles of radiation formation when using synchrotron sources and X-ray tubes differ significantly. For this reason other technical solutions have been proposed for SR sources that make it possible to obtain tomographic images. The Synchrotron radiation computed tomography (SRCT) method assumes that the sample rotates around the axis perpendicular to the X-ray flux (Fig. 5, a). a b Fig. 5. Schematics of setups, implementing the principle of tomography (a) and laminography (b) [12] Problems that arise when obtaining data from non-compact (non-isometric) samples can be avoided by using the method of Synchrotron radiation computed laminography (SRCL) which was proposed in 2005 by Helfen et al. [9]. Using a facility compatible with a stationary synchrotron source (ESRF, station ID19), they developed a method for collecting data on the structure of the analyzed object. The SRCL method combines the principles of laminography with the advantages of synchrotron imaging. Currently, it is used for non-destructive testing of non-isometric objects on a number of synchrotron radiation sources (ESRF, ANKA, Spring-8). When implementing the SRCL method, the rotary axis is deflected by an angle θ with respect to the direction of the X-ray beam (Fig. 5, b). This decision which affects the image quality makes it possible to reduce the distance from the sample to the detector. The tilt angle θ is determined experimentally. In this case the maximum rotation of the axis is usually limited by the design capabilities of the goniometer that holds and rotates the sample. The research results obtained using the SRCL method are comparable with the data that can be recorded by digital tomosynthesis [10, 11]. Helfen et al. thought that the SRCL method could be perceived as a more generalized version of the SRCT method [2]. Based on this fact and the similarity in the design of the equipment, the methods of computed laminography and tomography can be implemented on the same unit. Fisher et al. [13] demonstrated this possibility using a laboratory X-ray source. It was shown that tomographic research methods, including those based on the use of phase contrast [14], could also be applied to laminography. The method of computed laminography implies the need to use equipment which includes an X-ray source, a turntable with an inclined axis, a system of detectors and a computer with a software package for data processing. Depending on the task, technical solutions can be implemented that provide any additional effect (tensile, torsion, heating of the sample, impregnation of the fibrous composite, etc.). In the following sections of the paper, examples of the use of such setups are given. Resolution of synchrotron radiation computed laminography As mentioned earlier, when using tomography full access to the object under study is required, the size of this object is smaller than the size of the detector. Otherwise, the quality of the resulting image will deteriorate. This circumstance limits the application of the SRCT method to the study of large, nonisometric samples, such as plates. The reason for blurring (deterioration of quality) of the image and the appearance of artifacts is a lack of data that is required for accurate restoration of the section. Restoration of images in the absence of a certain fraction of data can be performed using the reciprocal space (threedimensional Fourier space) (Fig. 6) [2]. However, it should be taken into account that synchrotron computed
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