Electronic dose conversion technique using a NaI(Tl) detector for assessment of exposure dose rate from environmental radiation

An electronic dose conversion technique to assess the exposure dose rate due to environmental radiation specially from terrestrial sources was developed. For a 2×2 inch cylindrical NaI(Tl) scintillation detector, pulse-height spectra were obtained for gamma-rays of energy up to 3 MeV by Monte Carlo simulation. Based on the simulation results and the experimentally fitted energy resolution, dose conversion factors were calculated by a numerical decomposition method. These calculated dose conversion factors were, then, electronically implemented to a developed dose conversion unit (DCU) which is a microprocessor-controlled single channel analyzer with variable discrimination levels. The simulated spectra were confirmed by measurement of several monoenergetic gamma spectra with an multichannel analyzer. The converted exposure dose rates from the implemented dose conversion algorithm of DCU for the field test in the vicinity of the nuclear power plant at Kori as well as for standard sample sources were also evaluated, and the results were in good agreement with separate measurements by a high pressure ionization chamber within 6.4%