Na (511 keV, 1275 keV), 137 Cs (662 keV) à temperatura ambiente. Foram utilizados como fotosensores uma fotomultiplicadora (ET Enterprise, Modelo 9924SB, Inglaterra) e fotodiodo tipo PIN. Os cristais CsI:Tl apresentaram resposta à radiação com espectros de emissão característicos para cada tipo de fonte. Palavras-chave: cintilador, técnica de Bridgman, refino zonal, detectores de radiação ABSTRACT SUZART, K.F. Development and Characterization of the CsI:Tl crystal for use as a radiation detector. 2022. 98 p. Dissertação (Mestrado em Tecnologia Nuclear)-Instituto de Pesquisas Energéticas e Nucleares-IPEN/CNEN/SP. São Paulo.Scintillating materials are characterized by the emission of photons of visible or ultraviolet light when exposed to ionizing radiation, partially or totally absorbing the radiation. This work aimed to develop inorganic scintillator crystals in cesium iodide matrix using thallium ions (Tl + ) as dopant element with a concentration of 10 -3 M. A pure CsI crystal was grown for comparison purposes. Crystals were obtained using the Bridgman technique.The zonal refining technique was used in order to reduce the impurities found in the cesium iodide salt, obtaining a material as pure as possible. Satisfactory results were obtained with the purification of the material and the production of scintillating crystals. To detect such impurities and observe their decrease, the technique of optical plasma emission spectrometry (ICP-OES), was used, in ten parts of the ingot, after zonal refining. The CsI:Tl crystals were submitted to physicochemical characterization, such as: X-ray diffractometry to confirm the crystal lattice, transmittance of pure and thallium doped crystals, luminescence emission with maximum emission peak at 520 nm due to the presence of thallium. Distribution of the concentration of Tl along the crystal and optical microscopy to compare the surface of the crystal without polishing and with polishing. To evaluate the response of the scintillator crystals regarding their detector characteristics, experiments were carried out using sealed radioactive sources, namely: 133 Ba (80 keV, 355 keV), 60 Co (1173 keV, 1333 keV), 22 Na (511 keV, 1275 keV), 137 Cs (662 keV) at room temperature. A photomultiplier (ET Enterprise, Model 9924SB, England) and a PIN-type photodiode were used as photosensors.The CsI:Tl crystals showed a response to radiation with characteristic emission spectra for each type of source.