Which option is NOT among the three essential components for a semiconductor radiation detector?

• A. Semiconductor crystal
• B. Display screen
• C. Photocathode
• D. Amplifier

Answer: (C)

Semiconductor radiation detectors rely on a direct conversion process inside the crystal: incoming radiation creates charge carriers (electrons and holes) that are collected by an applied bias and then amplified and read out through electronics. The three core elements described—the semiconductor crystal as the active detecting material, the amplifier to boost the tiny signal, and the display or readout system to present the results—are what make this detection chain work.

A photocathode, on the other hand, belongs to vacuum-tube based devices that start with photoelectric emission: light hits the photocathode and ejects electrons, which are then amplified by subsequent stages. That mechanism is not how a solid-state semiconductor detector operates, so a photocathode is not a required component in this context.