Thermionic emission is the process by which electrons are emitted from the heated cathode.

Thermionic emission is the process by which electrons are emitted from the heated cathode.

• A. Thermionic emission
• B. Bremsstrahlung
• C. Fluorescence
• D. Secondary emission

Answer: (A)

Thermionic emission describes electrons escaping from a heated metal surface, such as the cathode filament, because the thermal energy provides enough energy to overcome the material’s work function. In radiography tubes, heating the filament makes electrons boil off to form a cloud that is then accelerated toward the anode to generate the X-ray beam. This distinguishes it from other terms: Bremsstrahlung is X‑rays produced by deceleration of electrons in the target, fluorescence is light emitted by a material after energy absorption, and secondary emission is electrons ejected due to incoming electrons hitting a surface, not due to heating. So the statement correctly identifies thermionic emission.

Thermionic emission describes electrons escaping from a heated metal surface, such as the cathode filament, because the thermal energy provides enough energy to overcome the material’s work function. In radiography tubes, heating the filament makes electrons boil off to form a cloud that is then accelerated toward the anode to generate the X-ray beam. This distinguishes it from other terms: Bremsstrahlung is X‑rays produced by deceleration of electrons in the target, fluorescence is light emitted by a material after energy absorption, and secondary emission is electrons ejected due to incoming electrons hitting a surface, not due to heating. So the statement correctly identifies thermionic emission.