Which element used in a flat-panel detector is able to convert x-ray photons directly into an electrical signal?

Which element used in a flat-panel detector is able to convert x-ray photons directly into an electrical signal?

• A. Cesium iodide
• B. Amorphous silicon
• C. Gadolinium
• D. Amorphous selenium

Answer: (C)

Direct conversion in flat-panel detectors uses a photoconductor that converts X-ray photons straight into electrical charge. Amorphous selenium fits this role, absorbing X-rays and generating electron–hole pairs that are collected to form an electrical signal, all without any light intermediate. The other materials are for indirect conversion: cesium iodide and gadolinium compounds act as scintillators, turning X-rays into visible light that is then detected by a silicon photodiode; and amorphous silicon is used as a photodiode that detects the light from a scintillator rather than directly sensing X-rays. So, the element that directly converts X-ray photons to an electrical signal is amorphous selenium.

Direct conversion in flat-panel detectors uses a photoconductor that converts X-ray photons straight into electrical charge. Amorphous selenium fits this role, absorbing X-rays and generating electron–hole pairs that are collected to form an electrical signal, all without any light intermediate. The other materials are for indirect conversion: cesium iodide and gadolinium compounds act as scintillators, turning X-rays into visible light that is then detected by a silicon photodiode; and amorphous silicon is used as a photodiode that detects the light from a scintillator rather than directly sensing X-rays. So, the element that directly converts X-ray photons to an electrical signal is amorphous selenium.