ASNT Industrial Radiography Radiation Safety Practice Test

What is the main use of the high-vacuum envelope in an X-ray tube?

1. To increase the X-ray intensity

2. To allow free electrons to travel without obstruction

3. To minimize heat production

4. To facilitate the exit of X-rays

The correct answer is: To allow free electrons to travel without obstruction

The primary function of the high-vacuum envelope in an X-ray tube is to allow free electrons to travel without obstruction. In an X-ray tube, electrons are generated and accelerated towards a target to produce X-rays. The presence of a vacuum is crucial because it eliminates air molecules that could impede the electrons' path. If air were present, electrons could collide with gas molecules, losing energy and being scattered before hitting the target, thus reducing the efficiency of X-ray production. Therefore, the vacuum facilitates a more direct and uninterrupted flow of electrons from the cathode to the anode, enabling the effective generation of X-rays. The other choices pertain to different aspects of X-ray tube qualities but do not define the unique role of the high-vacuum envelope as accurately.