ASNT Industrial Radiography Radiation Safety Practice Test

Why is tungsten used as the anode material in X-ray tubes?

1. It is lightweight

2. It has a low melting point

3. It has a high atomic number and melting point

4. It is inexpensive and readily available

The correct answer is: It has a high atomic number and melting point

Tungsten is utilized as the anode material in X-ray tubes primarily because it possesses a high atomic number and a high melting point. The high atomic number is significant because it enhances the tube's efficiency in producing X-rays. When electrons collide with the tungsten anode, a portion of their kinetic energy is converted into X-ray radiation. The efficiency of this conversion is greater with materials that have higher atomic numbers due to their increased density and the likelihood of interactions that produce X-rays. Moreover, tungsten’s high melting point (approximately 3,422 degrees Celsius or 6,192 degrees Fahrenheit) allows it to withstand the extreme heat generated during the rapid deceleration of electrons as they strike the anode. If a material with a lower melting point were used, it would risk damaging the anode and compromising the integrity of the X-ray tube under operational conditions. Therefore, the combination of high atomic number and exceptional heat resistance makes tungsten the ideal choice for this application.