What material constitutes the majority of the cathode in an X-ray tube?

The majority of the cathode in an X-ray tube is made of tungsten due to several important properties that make it ideal for this application. Tungsten has a very high melting point, around 3,420 degrees Celsius (6,192 degrees Fahrenheit), which is essential because the cathode must withstand the extreme heat generated during operation. When high-voltage electricity is applied, the tungsten filament emits electrons through a process called thermionic emission; as it heats up, it releases these electrons, which are then accelerated toward the anode to produce X-rays.

In addition to its high melting point, tungsten is dense and has a high atomic number (Z = 74), which contributes to effective X-ray production. The combination of these characteristics makes tungsten the preferred material for cathodes in diagnostic imaging and radiation therapy.

The other materials listed do not have the same combination of high melting point and efficient electron emission. For instance, aluminum has a much lower melting point and is typically used for filter materials rather than for the cathode itself. Copper, while a good conductor of electricity, lacks the melting point properties required for the high-temperature environment of the cathode. Silver, although it has excellent conductivity, is not used due to cost and its lower melting point