A radiation monitoring system with capability of gamma imaging and estimation of exposure dose rate

A new radiation monitoring system, which has the capability of both gamma imaging and estimation of real-time exposure dose rate, was developed by an integration of a visual image and a dose image. It is composed of a portable gamma imaging system for visualizing gamma-source distribution and a dose conversion unit (DCU) for real-time dose conversion from gamma spectrum. Using Monte Carlo simulation, gamma-ray spectra for energies from 10 keV to 5 MeV with energy intervals of 10 keV were calculated for a cylindrical NaI(Tl) detector used in our developed system. These calculated spectra were compared with the measured spectra for several monoenergetic gamma rays using a multichannel analyzer. Based on the simulation data and the dose conversion coefficients obtained from ICRU 47, the dose conversion factors were also calculated by matrix calculation. The feasibility of the DCU using the dose conversion factors was evaluated by measurement of exposure dose rates as a function of distance between the gamma ray and detector for several standard sources. The exposure dose rates measured by the DCU are within an 11.5% deviation with analytical values based on gamma factor. They are also similar to the dose rates measured by a high-pressure ionization chamber with maximum difference of six. We finally visualized two-dimensional distributions of gamma source and measured the exposure dose rate simultaneously.