Page "Scintillator" Paragraph 66
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* CsI ( Na ) or cesium iodide doped with sodium: the crystal is less bright than CsI ( Tl ), but comparable in light output to NaI ( Tl ).
The wavelength of maximum emission is at 420 nm, well matched to the photocathode sensitivity of bialkali PMTs.
It has a slightly shorter decay time than CsI ( Tl ) ( 630 ns versus 1000 ns for CsI ( Tl )).
CsI ( Na ) is hygroscopic and needs an air-tight enclosure for protection against moisture.
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