Research of objects with unilateral access is a promising area for the development of non-destructive testing systems. To create a real system and determine its optimal parameters, it is important to conduct preliminary computer simulations. The paper is devoted to creating a model of a non-destructive system based on backscattered X-rays in the Serpent Monte Carlo code. There are no known studies of the use of Serpent software to build such models. The purpose of the study was to confirm the possibility of detecting a defect, i.e., a material of a different density than the test object, which was placed in this object.
A model was created, the main components of which were the radiation source, the object under study, the defect, and the detector of backscattered radiation. Experiments were performed for several combinations of system parameters, in particular when changing the angle of illumination and the distance between the object and the detector. The energy of the radiation source used in the study was 100 keV. The test object of study was a steel plate, which contained a defect — a lead plate. Calculations were performed for six cases at illumination angles of 30 and 45 degrees (scattering angles of 120 and 135 degrees, respectively), and the distance between the object and the detector 1 and 5 cm. The detector was a plane that coincided with a NaI scintillation plate of 60 by 30 cm in size. It was conventionally divided into 1800 elements to detect the flux density of backscattered radiation.
A qualitative and quantitative analysis of the results met theoretical expectations. In particular, the Compton equation was fulfilled, which states that as the cosine of the scattering angle \theta increases, the energy of scattered radiation also increases. In the case of θ = 1200, the average flux density of backscattered radiation recorded by the detector was 1.1*10-3 units per square centimeter per second, and in the case of θ = 1350, this value was 7.9*10-4.
The results of the study can be used to build real non-destructive testing devices. These devices can be used in medicine, industry, and security systems. The model has some limitations. The radiation source in this model is monoenergetic, in contrast to classical X-ray systems, in which the radiation has a spectrum. Also, a defect is a plate of a large area, which is almost equal to the area of the object under study. For practical use, the device must be capable to detect a defect many times smaller than the object under study, such as a void in the weld, a tumor in the human body, or smuggled substances. The model can be improved in the future.
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