Determining the Concentration, Seasonal Changes and Shelf Life of Natural Radioactive Particles in the Air of Tehran

One of the most important challenges of nuclear accidents is the release and suspension of radioactive particles in the atmosphere. Knowing the behavior of these particles in the atmosphere will optimize management and subsequent decisions of unforeseen events. Using natural radioactive particles as environmental tracers to study atmospheric pollutants is one of the key and important studies in conducting atmospheric research. In order to determine the concentration of Pb-210, Bi-210 and Po-210 radionuclides, as well as to estimate the residence time of radioactive particles, sampling was done on a monthly basis from November 1400 to October 1401 in Tehran. The samples were taken by a high volume sampling pump with an average flow rate of 1.5 cubic meters per minute with a time interval of 6 to 12 hours and were prepared and counted in the Atomic Energy Organization. The results of the monthly average concentration of radionuclides show that the highest measured value for Pb-210 was 1.25 mBq/m3 in October. The average annual concentration for this parameter was around 0.89 mBq/m3, and its lowest value was recorded in April with a value of 0.42 mBq/m3. The results showed a relative increase in the concentration of this variable for April and May and a relative decrease for September and December. The average measured concentration for the variable  Po-210 in the whole period was about 0.058 mBq/m3. Also, 0.095 mBq/m3 in December is the highest concentration and 0.032 mBq/m3 in January is the lowest value measured for this radionuclide. The same trend was observed for Bi-210 with an overall average of 0.42 mBq/m3 for the period under review. The highest and lowest values measured for this radionuclide in the entire study period were 0.85 and 0.18 mBq/m3, respectively. According to the obtained results, based on Pb-210/Po-210, the average residence time of suspended particles was estimated to be 20.1 days. Based on this, July with an average of 22.5 days and January with an average of 17.8 days were estimated as the maximum and minimum length of stay measured in this research work. The obtained results can help in formulating the release and inhalation scenarios of radioactive particles caused by nuclear accidents.