The radiation-sensitive portion of a semiconductor detector is composed of which?

• A. Kyber crystal
• B. Light-emissive crystal
• C. Ionized air or gas
• D. Electron-emissive crystal

Answer: (D)

In a semiconductor detector, the active region must respond to ionizing radiation by generating charge carriers—electrons and holes—that can be collected to form an electrical signal. When radiation deposits energy in the crystal, electrons are promoted to the conduction band, creating free electrons that can be swept toward the electrodes under an applied electric field. This ability to release and mobilize electrons in response to radiation is captured by describing the material as electron-emissive.

That’s why the radiation-sensitive portion is described as an electron-emissive crystal. The other options don’t fit the concept: a kyber crystal isn’t a standard detector material; ionized air or gas implies a gas-filled detector rather than a solid-state semiconductor; a light-emissive crystal would primarily luminesce, not directly convert radiation into a collected electronic signal in a semiconductor detector.