In order to solve the problem of continuous or periodic monitoring of water areas affected by radioactive
contamination in the result of scheduled emissions in nuclear power plants or in the result of emergency situations in nuclear fuel cycle plants we need to develop measurement instruments with advanced mathematics
and program support to assess the level of radioactive contamination with required accuracy. The aim of theoretical research was to optimize detection device construction, estimate spectrometer metrological parameters in given measurement geometries, and determine effective position of detection device in the process of in situ measurements. This device consists of spectrometric scintillation probe packed into sealed container (detection device) based on NaI(T1) crystal of Ø 63 × 63 mm or Ø 63 × 160 mm size, cable reel with deep-sea cable and a tablet PC for data processing and displaying. The container withstands static hydraulic pressure up to 5 MPa and can be used for measurements at depths of 500 m maximum. Probe measures energy distribution of gamma-radiation with energy from 70 keV to 3000 keV. The implemented three-dimensional system for detection device position and orientation determination allows automatic operation of the device (without operator) for water areas or bottom sediment scanning. The spectrometer can output measurement results with three-dimensional geographical coordinates as index maps of distribution with necessary resolution and accuracy. Monte Carlo models of spectrometer and controlled objects are developed in order to determine the detector response functions to given radionuclides in given measurement geometries without use of expensive standard measures of activity. Multifunction gamma-spectrometer for in situ radiation monitoring of water areas and bottom sediments was developed and constructed. In the result of theoretical researches the response functions have been calculated in the form of theoretical spectra of monitored radionuclides in definite measuring geometries. The results of mathematical modeling of the gamma-emitting transfer process allowed to estimate effective position of detection device for in situ measurements of specific activity radionuclides 134Cs and 137Cs in bottom sediments
