Assessment of dose rate of detected gamma emitting nuclides using a carborne survey with a large volume NaI(Tl) detector

Abstract

A carborne survey system based on a hexahedral 4″ × 4" × 16″ NaI(Tl) detector was developed to assess the dose rate from ground deposited radionuclides over a wide area. A concept based on dose rate spectroscopy was introduced to the carborne survey to simply and directly calculate the ambient dose rate and dose rates of detected gamma emitting nuclides. In addition, an attenuation correction to account for loading the survey system in a vehicle was established, by calculating the count rate of several ROIs and the dose rate of natural radionuclides at diverse sites with different dose rates levels. All of the results from the carborne survey were then corrected to a dose rate 1 m above the ground in the air, to provide data consistency between diverse survey platforms. An experimental verification was conducted by comparing the dose rates of nuclides measured at the same site from the carborne survey and from in situ gamma-ray spectrometry at a fixed position using a portable HPGe detector. Finally, the developed method of a carborne survey was successfully applied to the evaluation of dose rate around the construction site of a nuclear facility. It is anticipated this result can be used to make a baseline of background radiations in the site before operating the nuclear facility currently under construction.