Function of the photocathode layer within a scintillation detector is to convert:

• A. x-rays into electrons
• B. electrons into x-rays
• C. light into electrons
• D. x-ray into more x-rays

Answer: (C)

The photocathode converts light into electrons. In a scintillation detector, X-rays interact with the scintillating material and produce flashes of visible light. Those light photons then strike the photocathode, which emits electrons via the photoelectric effect. Those electrons are carried into the amplification stages to generate a measurable electrical signal. The photocathode does not convert X-rays directly into electrons, nor does it convert electrons into X-rays or X-rays into more X-rays. Its job is to respond to the light produced by the scintillator and turn it into an electronic signal.