In direct capture detectors, which statement is true about amorphous selenium (A-Se)?

In direct capture detectors, which statement is true about amorphous selenium (A-Se)?

• A. It directly converts x-rays to charge
• B. It absorbs x-ray energy and then converts to light
• C. It requires scintillation layer
• D. It is used to store latent image

Answer: (A)

Direct capture detectors rely on a photoconductive material that converts x-ray energy directly into electrical charges. Amorphous selenium does this by absorbing x-ray photons and producing electron-hole pairs; under an applied electric field these charges are swept to electrodes, forming a charge pattern that corresponds to the x-ray exposure. This happens without any intermediate light emission, so no scintillation layer is needed. The readout then captures the resulting charge distribution to produce the image. Options that describe converting x-rays to light or requiring a scintillation layer refer to indirect detectors, not direct capture. While a latent image is represented by the stored charge, the key point here is that A-Se directly converts x-rays to charge, making that statement the best description of its role.

Direct capture detectors rely on a photoconductive material that converts x-ray energy directly into electrical charges. Amorphous selenium does this by absorbing x-ray photons and producing electron-hole pairs; under an applied electric field these charges are swept to electrodes, forming a charge pattern that corresponds to the x-ray exposure. This happens without any intermediate light emission, so no scintillation layer is needed. The readout then captures the resulting charge distribution to produce the image.

Options that describe converting x-rays to light or requiring a scintillation layer refer to indirect detectors, not direct capture. While a latent image is represented by the stored charge, the key point here is that A-Se directly converts x-rays to charge, making that statement the best description of its role.