Speaker
Description
With the rapid development of advanced manufacturing industries, there is a great demand for high-resolution imaging methods applicable for metal materials in the field of nondestructive testing (NDT). Due to the large focal spot and broad spectrum characteristics of a bremsstrahlung-based gamma-ray source, the resolution of the traditional absorption-based gamma-ray imaging method is limited to the submillimeter level, which cannot meet the urgent requirement of high-resolution imaging for metal materials in NDT. Hence, it is necessary to develop novel gamma-ray imaging modalities for this application.
Using the phase shift information of an imaging object, the phase contrast imaging (PCI) has been proved to be an excellent imaging method for low Z materials in the X-ray energy since the phase-shift cross-section is about 2-3 orders higher than the absorption cross-section. Our preliminary study shows that the PCI also has advantages for metal material imaging in the gamma-ray region, since a maximum cross-section ratio between the phase-shift and the absorption can be obtained for metal materials in the MeV energy region. Meanwhile, the intrinsic edge enhancement characteristics in in-line PCI can help to discriminate the material interfaces, which can be used to identify the holes, cracks, etc. Hence, gamma-ray PCI provides a novel way for high-resolution imaging for metal materials.
To realize gamma-ray PCI, the prerequisite is a gamma-ray source characterized by high spatial coherence. The advent of an inverse Compton scattering (ICS) light source, based on the interaction of relativistic electrons and high-intensity laser, provides an excellent prospect for the gamma-ray PCI, since it can provide quasi-monochromatic, energy tunable, high brightness, and high coherent gamma-rays.
To demonstrate the feasibility of gamma-ray PCI, we have developed a simulation method of gamma-ray PCI for metal samples based on the very compact ICS gamma-ray source (VIGAS) facility under construction in Tsinghua University, which is designed to provide quasi-monochromatic gamma-rays in the 0.2 – 4.8 MeV energy region for advanced radiation imaging applications [1]. The effects of finite focal spot, energy dispersion, and other physical properties of the VIGAS are considered in the simulation. Using the simulation method, a phantom of concentric tungsten–aluminum spheres is simulated. Compared to conventional absorption imaging, clear edge enhancement is witnessed in the PCI image, which will facilitate the identification of the material interface. The simulation results prove the feasibility of gamma-ray PCI for metal samples.
This research is supported in part by the National Natural Science Foundation of China (No. 12027902).
[1] J.Y. Sun, Z.J. Chi, Y.C. Du, R.K. Li, W.H. Huang, C.X. Tang, A simulation method of gamma-ray phase contrast imaging for metal samples, Nucl. Instrum. Methods Phys. Res. A 1053 (2023) 168321.
