X-ray technology plays a crucial role in numerous fields, including medical diagnosis, non-destructive testing, security screening, and scientific research. Its performance largely depends on the primary materials used in the generation and detection processes. These materials must possess specific atomic numbers, densities, crystal structures, and stability to ensure the effective generation, transmission, modulation, and reception of X-rays.
Regarding X-ray sources, the core material is a high-atomic-number metallic target, commonly including tungsten (W), molybdenum (Mo), and chromium (Cr). Tungsten, due to its high melting point, good thermal conductivity, and ability to produce high-energy continuous and characteristic spectra, has become the mainstream target material for medical and industrial flaw detection X-ray tubes. Molybdenum can produce characteristic radiation suitable for soft tissue imaging at lower tube voltages and is often used in special diagnostic scenarios such as mammography. Chromium is used in specific fluorescence analysis and low-energy X-ray devices. The purity and grain orientation of the target material affect the intensity and energy spectrum distribution of X-rays; therefore, strict control of metallurgical and processing techniques is required during preparation.
In the field of X-ray detection, the main materials are divided into two categories: scintillators and semiconductor detector materials. Scintillators, such as sodium iodide (NaI), cesium iodide (CsI), and cadmium tungstate (CdWO₄), convert X-ray photon excitation into visible light, which is then read by photomultiplier tubes or photodiodes. These materials must possess high luminous efficiency, fast decay time, and good linear response, and exhibit a certain degree of resistance to deliquescence and mechanical shock. Semiconductor detector materials, represented by cadmium zinc telluride (CZT), cadmium telluride (CdTe), silicon (Si), and germanium (Ge), utilize photons to directly generate electron-hole pairs and convert them into electrical signals. They offer advantages such as high energy resolution and fast response, making them suitable for nuclear medicine imaging and high-precision energy dispersive spectroscopy analysis.
Furthermore, heavy metals and alloys, such as lead (Pb), barium (Ba), and lead-containing polymers, are widely used in X-ray optics and filtering systems. Their high atomic number and high density characteristics enable X-ray shielding and beam hardening, reducing the impact of low-energy scattering on image quality. Regarding window materials for X-ray tubes, beryllium (Be) is widely used due to its low atomic number, good transmissivity, and mechanical strength, ensuring X-ray transmission while maintaining a vacuum seal.
Overall, the selection of primary X-ray materials revolves around high atomic number, suitable density, stable physicochemical properties, and compatibility with process requirements. The combination and optimization of different materials determine the imaging performance, detection sensitivity, and lifespan of the X-ray system, forming the material basis for the widespread application of this technology.
