Thallium doped cesium iodide is one of the brightest scintillators with the fluorescence spectrum with maximum at 550 nm, which allows using photodiodes for detection of the emission. Because a scintillator-photodiode pair can be used, it is possible to reduce significantly the size of the detection system, to do without a high-voltage power supply, and to use the detection system in magnetic fields. CsI(Tl) has a high effective atomic number and consequently larger cross-section of the gamma-radiation photoabsorption.
For practical application, it is very important that CsI(Tl) is not hygroscopic. With relatively good radiation hardness (103 rad) it is applied in high-energy physics. Depending on growth conditions CsI(Tl) crystals can be obtained with low afterglow for application in tomographic systems.