Abstract
This paper examines the equilibrium and disequilibrium states of radionuclides of the radium decay series. The study of radionuclide activity relative to the parent isotope (238U) made it possible to identify several regularities. Within the southern regions of the Republic of Kazakhstan – namely the Yenisey-Altai-Sayan, Zhetysu Alatau-Tian Shan, Central Kazakhstan, and Scythian-Turan hydrogeological regions – the 234Th / 238U ratio varies widely (from 0,004 to 133,6). It is characteristic that at low uranium concentrations (0,58 mg/L), the activity of thorium isotopes significantly predominates (234Th / 238U>1), whereas an increase in the concentration of the parent isotope is accompanied by a decrease in the specific activity of 234Th, and the ratio becomes less than unity. A similar trend is observed for 230 Th, 210 Pb, and 210 Po. In contrast, 226Ra shows a chaotic distribution without clear dependencies. The widespread supersaturation of groundwater with 222Rn up to 5550 Bq/L is a consequence of the intensive migration of this gas from the emanating reservoir during the decay of parent nuclides.