Why is CsI preferred over ZnCdS?

The preference for Cesium Iodide (CsI) over Zinc Cadmium Sulfide (ZnCdS) in certain applications is primarily due to CsI's greater crystal packing density and better absorption characteristics. CsI is known for its ability to effectively convert incident x-ray or radiation energy into visible light, which is a crucial aspect of detectors used in fluoroscopy and other imaging applications.

The crystal structure of CsI allows for a more compact arrangement of atoms, which enhances its ability to absorb and convert x-ray photons efficiently. This results in a higher yield of visible light per unit of radiation exposure, leading to improved image quality and sensitivity in imaging systems. Such performance is particularly important in environments where clarity and detail are critical.

While the other options may present certain advantages in their respective contexts, they do not provide the same level of effectiveness in terms of absorption and light output as CsI. Therefore, the characteristics of CsI in terms of crystal packing density and absorption make it the preferred choice over ZnCdS for imaging applications.