Background and Objective: Due to importance of ionizing radiation on human health, many studies have been performed to measure the background gamma radiation all around the world as well as some cities in lran. This study was carried out to measure the amount of background gamma radiation in outdoor areas in different seasons in Zanjan to determine the annual effective dose of the city residents.
Materials and Methods: To determine the dose rate of background gamma radiation in outdoor areas, 8 stations (4 in the main directions and 4 in the downtown areas) were selected using the map of the city. Eight measurements were performed for each station (twice in each season) using Geiger-Muller detector (RDS-110) calibrated by Cs-137.
Results: The mean value of dose rate and the annual effective dose due to background gamma radiation in different season in Zanjan were determined 126 nGy/h and 0.15 mSv respectively. The minimum and maximum mean values of dose rate were found 120±21 nGy/h and 134±18 nGy/h in summer and spring respectively.
Conclusion: The results show that the dose rate and the annual effective dose for the city residents due to the background gamma radiation in outdoor areas is twice as much as international mean value reported by UNSCEAR-2000. To determine the total annual effective dose of Zanjan residents, measuring the dose rate in indoor areas is necessary.