What component of the image intensifier emits electrons?

• A. The output phosphor
• B. The photocathode
• C. The input phosphor
• D. The glass envelope

Answer: (B)

The correct choice is the photocathode, which is a vital component of the image intensifier system. The photocathode is responsible for converting incoming light photons, produced by the input phosphor, into electrons. When x-rays interact with the input phosphor (typically made of cesium iodide or sodium iodide), it emits visible light. This light then strikes the photocathode, resulting in the emission of electrons due to the photoelectric effect.

These emitted electrons are then focused and accelerated toward the output phosphor, enhancing the overall efficiency and brightness of the image being produced. This process is crucial for improving image quality during radiographic procedures, making the photocathode an essential element in the functioning of the image intensifier. The other components, like the input phosphor and output phosphor, serve different roles in the system, such as converting x-rays to light and enhancing brightness, respectively. The glass envelope protects the internal components but does not play a direct role in electron emission.