The article describes the problems of creating a scintillation spectrometer with a CsI:Tl crystal to replace spectrometers with NaI:Tl crystals which are widely used at nuclear power plants (NPPs) to monitor the activity of air, waste water and adjacent territories. The advantages of CsI:Tl-spectrometers are in the best energy resolution; much greater resistance to mechanical and electromagnetic influences due to the use of silicon photomultipliers (SiPM) instead of vacuum photomultiplier tubes (VPMT); much greater durability due to the very low hygroscopicity of the material. The strong mismatch between the emission spectrum of the crystal and the spectral sensitivity of the VPMT photocathodes, the relatively long decay time and the complex, multicomponent form of the light flash made spectrometers with CsI:Tl crystals not competitive. The paper describes the methods of constructing a spectrometer, which made it possible to realize the useful properties inherent in a crystal and to level its disadvantages. As a result of the cycle of research and development work, the Stark-02 intellectual detector has been designed and described. Typical relative energy resolution with crystals of volume 45 cm3 at an energy of 662 keV of the 137Cs source is better than 6.5% in the ambient temperature range Q = +10 ÷ +45 °C and not worse than 7.5% in the extended range Q = -25 ÷ +55 °C.