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Caesium iodide or cesium iodide (chemical formula CsI) is the ionic compound of caesium and iodine. It is often used as the input phosphor of an X-ray image intensifier tube found in fluoroscopy equipment. Caesium iodide photocathodes are highly efficient at extreme ultraviolet wavelengths.
Caesium iodide atomic chains can be grown inside double-wall . In such chains I atoms appear brighter than Cs atoms in electron micrographs despite having a smaller mass. This difference was explained by the charge difference between Cs atoms (positive), inner nanotube walls (negative) and I atoms (negative). As a result, Cs atoms are attracted to the walls and vibrate more strongly than I atoms, which are pushed toward the nanotube axis.
Caesium iodide is used as a beamsplitter in Fourier transform infrared (FTIR) spectrometers. It has a wider transmission range than the more common potassium bromide beamsplitters, working range into the far infrared. However, optical-quality CsI crystals are very soft and hard to cleave or polish. They should also be coated (typically with germanium) and stored in a desiccator, to minimize interaction with atmospheric water vapors.
In addition to image intensifier input phosphors, caesium iodide is often also used in medicine as the scintillating material in flat panel x-ray detectors.
Properties
+Solubility of Csl in waterHaynes, p. 5.191
!Т (°C)
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S (wt%) 30.9 37.2 43.2 45.9 48.6 53.3 57.3 60.7 63.6 65.9 67.7 69.2
Applications
An important application of caesium iodide crystals, which are , is electromagnetic calorimetry in experimental particle physics. Pure CsI is a fast and dense scintillating material with relatively low light yield that increases significantly with cooling, and a fairly small Molière radius is 3.5 cm. It exhibits two main emission components: one in the near ultraviolet region at the wavelength of 310 nanometer and one at 460 nm. The drawbacks of CsI are a high temperature gradient and a slight hygroscopicity.
(2025). 9781461450665, Springer. ISBN 9781461450665
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