Using 226Ra/228Ra disequilibrium to determine the residence half-lives of radium in vegetation compartments

The concentrations of 226Ra and 228Ra were studied in different vegetation compartments and in available and non-available soil fractions in a Mediterranean scrubland ecosystem. A high percentage of the plant samples showed an apparent discrimination in favour of 226Ra over 228Ra. A linear compartmental model was applied to the soil–plant system. It allowed us to explain why these discrimination coefficients differed from unity, to obtain the residence half-lives of radium in the different compartments, to estimate the age of the plants, and to simulate the temporal evolution of the radioactive concentrations in each compartment.