Home – Home – Jornals – Chemistry for Sustainable Development 2003 number 6

On the basis of simultaneous gamma spectroscopic determination of radionuclides of the uranium series (²³⁸U, ²²⁶Ra, ²²²Rn, ²¹⁰Pb) and isotopes arriving from the atmosphere (²¹⁰Pb_atm and ¹³⁷Cs) in rocks and bottom sediments, radiogeochemical background of land sediments represented mainly by granitoid weathering products was obtained (35-55 Bq/kg), along with evidences of the hydrodynamic mode of sediment formation within the recent century. Three types of radioactivity anomalies exceeding the background by one-two orders of magnitude were revealed on the southern bank of the lake: natural uranium and radium anomalies; industry-related radium anomalies (ash obtained from burning uranium-bearing coal); industry-related uranium anomalies. Sedimentation rate was estimated in the deep water region using the decay of ²¹⁰Pb_atm activity to be 0.2-0.4 mm/year during the recent century. On the basis of uranium to radium ratio, it was established that the fraction of uranium in deep water sediments arriving from the lake water is 1.5-2 times higher than the fraction arriving with the suspension. One of the sources of uranium in the lake water was erosion of uranium-bearing coal within the geological time scale. A layer enriched with radium was discovered near the bank at the depth of 5 to 20 cm. The presence of high-temperature mineral mullite in the sediment is an evidence of the penetration of industry-related radioactive ash into the lake in amounts that can hardly be dangerous for the biogeosystem of the lake Ysyk-Kul.