Preconcentration activation analysis of uranium and thorium in standard reference materials and food

Uranium and thorium, the two naturally occurring radionuclides, are well known for their radiotoxicity as well as chemical toxicity when present at high levels. In human body, uranium is known to concentrate in kidney and bone whereas thorium accumulates in liver and bone. Environment in general and food in particular are the major sources of these two elements. It is therefore important to measure concentrations of uranium and thorium in food samples along with other materials of interest and to calculate their average daily intakes. Uranium and thorium content of food are rather difficult to measure because of their very low levels; viz., <10 ppb. In the past, preconcentration methods followed by alpha spectrometry or fluorometry have been used for their determinations in a number of matrices. Gamma spectrometry of neutron-activated samples preceded by coprecipitation has also been employed. These methods generally involve a number of steps and are not necessarily very sensitive. A simple and rapid method for the separation of uranium and thorium has been developed in this study, and neutron activation analysis (NAA) has been used for their determinations.