374 



The concentrations of natural radionuclides (uranium-238 and radium-226) in the 

 investigated samples of water from the rivers of the Mirny Rayon are within the mezui 

 values of long-term laboratory observations (since 1983) (for the Vilyuy River, the 

 concentration of uranium fluctuated within the range of 0...[illegible] 0.5 pCi/1, for 

 radium-226 it was 0.2-0.3 pCi/1), which is slightly below the average values for the 

 Republic, which are 0.4 pCi/1 for radium-226, and 0.5 pCi/1 for uranium-238. 



Artificial radionuclides enter open bodies of water mostly by being washed out of 

 the soil by rain and thawing waters. 



The concentration of cesium-137 in all water samples was below the minimum 

 measurable activity or lower than 0.5 pCi/1. 



The content of strontium-90 in the individual samples of water collected from the 

 rivers of the Mirny Rayon is more compa: able with the results of long-term observations 

 of water in the lakes of the Vilyuysk group of rayons, where the concentration of 

 strontium-90 fluctuated within the range of 1.5-3.5 pCi/1, while in the rivers it was 0.5-1.5 

 pCi/1. 



It would be premature to declare the estimate final because of an insufficient 

 number of samples, and work on investigating the level of strontium-90 in these specific 

 sectors must be continued. 



In general, the concentration of natural (uranium-238, radium-226) and artificial 

 (strontium-90, cesium- 137) radionuclides in the investigated samples of water from the 

 rivers of the Mirny Rayon is at least 100 times lower th£Ln permissible concentrations for 

 category B under the Standards of Radiation Safety (NRB-76/87). 



G.Ye. Semonov 



Head of the Department of Radiation Hygiene 



of the Yakut Republic Sanitation 



and Epidemiology Station 



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