[ RadSafe ] Fractionation of Uranium Isotopes in Nature

[Orthen, Rick]

To add to Bob's spot-on evaluation:

The State of California and the USEPA have suggested other
mass-to-activity conversion factors (0.79 pCi/ug and 1.3 pCi/ug,
respectively) reflecting higher relative abundances of 234U to 238U.
The mass of uranium in water is largely determined by 238U, due to its
longer half-life, while the total activity in the water is determined by
the activity of all uranium isotopes. In natural water, the 234U is
slightly more soluble causing the activity ratio of 234U to 238U to vary
from 1:1 to more than 20:1. Consequently, accurate conversion from mass
to activity or vice versa requires knowledge of the concentration of
each of the three uranium isotopes.

Rick Orthen
CEC Inc.