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CsI(Tl)Crystal & Array

Cesium iodide crystals can be divided into three types based on the dopant, CsI(Tl), CsI(Na) and pure CsI. All of them are colorless transparent cubic crystals. CsI(Tl) is the most typical alkali halide scintillation crystal apart from NaI(Tl). Its light output is 45% of that in NaI(Tl). Its emission spectrum has a broad band at 350-700nm and a peak at 550nm. Its emission spectrum can match well with SPD so that the read out system can be simplified. Since the decay time is dependent on the ionization capacity of a particle, it is suitable to detect heavy charged particles under strong -ray background. The luminescence efficiency of CsI(Na) is similar to that of NaI(Tl) crystals. The emission spectrum peaked at 420nm can match well with PMT. Its temperature dependence is small and can be applied in high temperature and outer space environment. However, its disadvantage is that the luminescence decreases quickly in the low energy (less than 20 KeV) and hygroscopicity is stronger than that of CsI(Tl).Pure CsI crystal is much less hygroscopic than CsI(Tl). Its emission consists of the fast intrinsic luminescence (10ns) peacked around 305nm and a slow component (100-4000ns) around 350-600nm. After intensive efforts to suppress the slow component, the fast/slow ratio can reach as large as four. The total light output is as large as 4-5% of NaI:Tl. The possible application of this crystal lies its fast timing characteristics. In late 1990’s ,SICCAS become the main supplier of CsI for the BaBar experiment at standford Linear Accelerator Center(SLAC) and Belle experiment at High EnergyAccelerator Research Organization(KEK). The BEPCⅡexperiment run by IHEP in Beijing  also used CsI from SICCAS. Morever, we can fabricate CsI(Tl) at both linear and  2D arrays with pixel sizes as small as 0.3x0.3x0.3mm.

Scintillation properties of CsI-based crystals

Properties
CsI(Tl)
CsI:Na
CsI
Densityg.cm-3
4.53
4.51
4.51
Radiation length(cm)
1.86
1.86
2.43
Decay constant(us)
1.0
0.63
16
Emission peak(nm)
550
420
315
Light yield(%NaI:Tl)
47
85
4-6
Melting point(°C)
621
621
621
Hardness(Mho)
2
2
2
refractive Index
1.78
1.84
1.95
Hygroscopicity
slightly
Yes
Slightly
Cleavage
none
none
none

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