Analysis of U and Th in soils and sediments B—Why do we sometimes get the WRONG RESULT?

In 1978, the National Bureau of Standards began a program to develop environmental-level natural matrix radionuclide Standard Reference Materials for the evaluation of analytical methods. A customer reported a −15 % difference between their value and the certified uranium massic concentration in SRM 4353 (Rocky Flats Soil B I). This report prompted an investigation using several independent methods to confirm the certified uranium value. Investigation indicated the discrepancy to be due to a highly insoluble minor mineral fraction that contained high concentrations of uranium. The suspect mineral, zircon, is widespread in soils and sediments and represents an analytical complication.