Development and characterization of CsI (Tl) crystal for use as a radiation detector

Cesium iodide crystal activated with thallium (CsI(Tl)) is used as radiation sensor because of its favorable characteristics as scintillator, when excited by gamma radiation. This crystal has good mechanical strength and it is relatively little hygroscopic. In the present work, the CsI(Tl) crystal was grown in the Nuclear Energy Research Institute (IPEN/CNEN/SP) by Brigdman technique, in two different formats: (a) cylindric ( ∅ 20.1 mm x ­ 11.9 mm) and (b) parallelepiped ( c 12.3 mm x ­ 19.5 mm). The scintillator response was studied through five gamma radiation sources: 99m Tc (140 keV), 137 Cs (662 keV), 60 Co (1173 keV, 1333 keV) and 22 Na (511 keV, 1275keV). The crystals were coupled to a photomultiplier tube using 0.5 McStokes viscosity silicone grease as the optical interface. All electronics for signal measurements were developed at IPEN. Luminescence property of the CsI(Tl) crystal was excited by the radiation from a 99m Tc source. The energy resolution of the crystalline detector was determined by the FWHM parameter, corresponding to the photopeak width at half of its height. Gamma radiation was spectrometry performed with the following sources: 99m Tc , 241 Ba, 137 Cs, 60 Co and 22 Na.