CsI(Tl) has a light output of 54 photons/keV and is one of the brightest scintillators known. It has most of its emission in the long wavelength part of the spectrum (>500nm), it is well-suited for photodiode readout.
CsI(Tl) has very good stopping power, is slightly hygroscopic and with good plastic mechanical properties. Combined with a relatively good radiation hardness properties, CsI(Tl) is also well suited for High Energy Physics. It is used in Phoswiches for whole body counting and X-ray astronomy as the "guard crystal" with typically a thin NaI(Tl) as the primary detector. It also has no cleavage plane and is quite rugged – which makes it well-suited for well-logging, space research or other applications where severe shock conditions are encountered.
|Melting point [K]||894|
|Thermal expansion coefficient [C-1]||54 x 10-6|
|Wavelength of emission max. [nm]||550|
|Lower wavelength cutoff [nm]||320|
|Refractive index @ emission max||1.79|
|Primary decay time [ns]||1000|
|Light yield [photons/keVγ]||54|
|Photoelectron yield [% of NaI(Tl)] (for γ-rays)||45|
Cesium Iodide can also be Sodium activated (Na) or undoped (Pure)
CsI(Na) has a wavelength of emission peak at 420nm and has a light output of 85% of NaI(Tl). Compared to NaI(Tl), the material interesting where severe environmental conditions are encountered. It is used in Oil and gas exploration – well logging, Space research and other harsh environment applications.
CsI(Pure) has an emission maximum at 315 nm with an intensity much smaller than either of the activated types of this material. But, this emission is characterized by a relatively short decay time of 16 ns, thus the material can be used for fast timing applications. Undoped CsI is mainly used in physics experiments because of its combination of fast timing and relatively high density.
These material variations are not standard production but can be considered for large projects.