Which description defines thermionic emission?

Which description defines thermionic emission?

• A. The emission of electrons from heated tungsten filament in the x-ray tube
• B. The emission of gamma rays from the target
• C. Ionization of ambient air
• D. Acceleration of electrons in the anode

Answer: (A)

Thermionic emission is the emission of electrons from a heated metal surface. In an x-ray tube, heating the tungsten filament provides enough energy for electrons to overcome the work function and escape into the tube. Those electrons are then pulled toward the positively charged anode by the high voltage, forming the current that produces x-rays when they strike the target. Gamma rays from the target result from interactions of electrons with the target, not from the filament itself. Ionization of ambient air would be air ionization, not emission from the heated filament. Acceleration in the anode happens after emission, not the emission process itself.

Thermionic emission is the emission of electrons from a heated metal surface. In an x-ray tube, heating the tungsten filament provides enough energy for electrons to overcome the work function and escape into the tube. Those electrons are then pulled toward the positively charged anode by the high voltage, forming the current that produces x-rays when they strike the target. Gamma rays from the target result from interactions of electrons with the target, not from the filament itself. Ionization of ambient air would be air ionization, not emission from the heated filament. Acceleration in the anode happens after emission, not the emission process itself.