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

Amorphous selenium is the element that is specifically designed to convert x-ray photons directly into an electrical signal in flat-panel detectors. This conversion process occurs because amorphous selenium has excellent properties that allow it to absorb x-ray radiation efficiently. When it absorbs the x-ray photons, it generates electron-hole pairs, which then can be collected as an electrical signal. This direct conversion method facilitates high image resolution and quality in digital radiography, making it a preferred material for applications requiring precise imaging.

While there are other materials like amorphous silicon used in flat-panel detectors, these typically require an additional conversion step involving a scintillator to first convert x-rays to visible light before generating an electrical signal. Elements such as copper and gallium arsenide are not primarily used for x-ray photon conversion in this context. Copper is used in wiring and connections within the detector but does not play a role in direct conversion, while gallium arsenide is more commonly associated with specific types of detectors that may not be designed to directly convert x-ray photons in the same manner as amorphous selenium.