The uranium isotopes 238U, 235U and 234U are found
naturally in the environment. 238U and 235U are parent nuclides of two
independent decay series of isotopes, while 234U is a member of the
238U decay chain. When decay series occur in a closed system the series tends
to reach, with time, the state of secular equilibrium in which the activities of all series
members are equal to the activity of its first nuclide. The activity ratio
234U/238U in natural uranium may vary as a consequence of decay
chain disequilibrium due to alpha recoil and biogeochemical processes. A study based on
measurement of uranium concentration and 234U/238U activity ratios in
soil samples collected from Nalgonda district, Andhra Pradesh, India, a proposed mining
site, was carried out to find the spatial distribution of uranium and the state of secular
equilibrium of 234U/238U to examine the possibility of applying
uranium concentration and uranium isotopic activity ratios to detect any hydrogeochemical
changes in the environment during/post-operation. Soil samples were collected and analyzed
for uranium concentration using the conventional UV fluorimetric method, showing a uranium
concentration in the range of 0.7 ± 0.2 ppm to 7.9 ± 0.4 ppm with an average of 3.4 ppm, and
234U/238U activity ratios were estimated using the alpha
spectrometry technique, showing an activity ratio in the range of 0.92 ± 0.11 to
1.02 ± 0.11. The 234U/ 238U activity ratio obtained indicated that
these two uranium isotopes are in the state of secular radioactive equilibrium. The percent
activity ratio of 238U/total U and 234U /total U is observed to vary
from 47.94 ± 4.83 to 50.76 ± 4.87 and 45.80 ± 3.83 to 49.14 ± 3.99, respectively.