ASNT Industrial Radiography Radiation Safety Practice Test

What effect does increasing milliamperes across the filament have in an X-ray tube?

1. It decreases the lifespan of the tube

2. It reduces the amount of radiation produced

3. It increases the number of free electrons available

4. It lowers the operating temperature

The correct answer is: It increases the number of free electrons available

Increasing milliamperes across the filament in an X-ray tube results in a rise in the number of free electrons available. This occurs because the milliamperes represent the current flowing through the filament, which heats it up. When the filament is heated to a certain temperature, it causes the electrons to gain enough energy to escape from the surface of the filament, creating a cloud of electrons. As the filament temperature increases with higher milliamperes, more electrons become available for the process of electron emission, thereby increasing the electron current that is available to be drawn toward the anode. This, in turn, enhances the production of X-rays when these electrons are accelerated and collide with the anode target. Therefore, the correct answer is that increasing the milliamperes leads to a higher number of free electrons in the system, which is crucial for effective X-ray production.