Why is tungsten (W) used as the target material in x-ray tubes?

• A. Low cost, availability, and malleability
• B. High atomic number, high melting point, and high thermal conductivity
• C. Lightweight, flexibility, and ductility
• D. Non-reactive, low thermal expansion, and abundance

Answer: (B)

Tungsten is selected as the target material in x-ray tubes primarily due to its high atomic number, high melting point, and high thermal conductivity. The high atomic number is significant because it increases the efficiency of x-ray production; materials with higher atomic numbers are more effective at producing x-rays when bombarded with electrons, resulting in a greater number of x-ray photons being generated.

The high melting point of tungsten, which is around 3,422 degrees Celsius, is crucial because the target in an x-ray tube is exposed to intense heat generated by the kinetic energy of incoming electrons. A material with a high melting point can withstand this heat without deforming or vaporizing, ensuring the longevity and reliability of the x-ray tube.

Additionally, tungsten's high thermal conductivity allows for efficient heat dissipation. This property helps to spread out the heat generated during x-ray production, preventing localized overheating that could damage the x-ray tube system and ensuring continuous operation.

In contrast, the other options do not provide the necessary characteristics critical to the performance of x-ray tubes. While cost and availability are relevant factors for materials in general, they do not address the specific technical requirements for an effective target material in x-ray production. Similarly, lightweight and flexibility do not pertain