What are the Crystals made of?

What are the Crystals made of?

• A. Sodium iodide w/ thallium trace added to increase light production
• B. Cesium iodide
• C. Sodium bromide
• D. Selenium

Answer: (A)

Scintillation crystals in X-ray detectors are chosen for their ability to convert incoming X-ray energy into visible light that a detector can read. Sodium iodide doped with thallium is the classic material for this purpose. The iodine provides strong X-ray absorption (dense, high atomic number), while the thallium acts as an activator that creates luminescent centers, producing a bright, fast light flash when excited by X-rays. That light is then detected by photodetectors to form the image. While cesium iodide is also used as a scintillator in some detectors, and selenium serves as a photoconductor in direct-conversion detectors, sodium iodide with thallium remains a standard because of its high light yield and well-understood performance. Sodium bromide is less common for this role.

Scintillation crystals in X-ray detectors are chosen for their ability to convert incoming X-ray energy into visible light that a detector can read. Sodium iodide doped with thallium is the classic material for this purpose. The iodine provides strong X-ray absorption (dense, high atomic number), while the thallium acts as an activator that creates luminescent centers, producing a bright, fast light flash when excited by X-rays. That light is then detected by photodetectors to form the image.

While cesium iodide is also used as a scintillator in some detectors, and selenium serves as a photoconductor in direct-conversion detectors, sodium iodide with thallium remains a standard because of its high light yield and well-understood performance. Sodium bromide is less common for this role.