Which of the following materials is used as an added filter in x-ray tubes?

Aluminum is widely used as an added filter in x-ray tubes due to its effective attenuation properties. The primary purpose of the added filter is to reduce the intensity of low-energy x-ray photons, which contribute little to the diagnostic quality of an image and increase patient radiation dose. By filtering these low-energy photons out, aluminum enhances the beam quality, allowing for better penetration and improved image clarity.

In addition to effectively reducing the dose to the patient, the use of aluminum helps to ensure that the x-ray beam is more homogeneous, which is crucial for accurate imaging and evaluation. The atomic number of aluminum is optimal for this application, providing a balance between filtration efficiency and image quality. Consequently, its use in x-ray machines is a standard practice in radiographic procedures.