Entrance phosphor

Last revised by Raymond Chieng on 28 Feb 2023

The entrance phosphor (or input phosphor) is a component of the image intensifier in fluoroscopic systems that converts the energy from x-rays into light photons. It is composed of a fluorescent material such as cesium iodide activated with sodium (CsI:Na) and coats the entrance surface of the image intensifier. The light produced by the entrance phosphor subsequently travels to a photocathode layer 1.

In earlier days Zinc-cadmium sulfide activated with Silver was used as the material for input phosphor, but CsI:Na was subsequently used as it provides better image quality owing to its high packing density, favorable atomic number and vertical orientation of crystals 1.

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