DETERMINATION OF URANIUM AND THORIUM CONCENTRATIONS IN SOILS - COMPARISON OF ISOTOPE-DILUTION SECONDARY ION MASS-SPECTROMETRY AND ISOTOPE-DILUTION THERMAL IONIZATION MASS-SPECTROMETRY

The purpose of the present study existed in making a comparison between isotope dilution-thermal ionization mass spectrometry (ID-TIMS) and isotope dilution-secondary ion mass spectrometry (ID-SIMS) on the basis of their precision and accuracy. Three different sets of soils were therefore analyzed to determine their uranium and thorium contents. An analysis of variance (ANOVA) demonstrated that the precision of TIMS was about 8 times better than that of SIMS. It was clear in the case of TI MS that the overall precision can almost completely be explained by the variation in composition between samples, while for the SIMS analyses, the instrumental error plays an important role in determining the precision. The overall SIMS/TIMS ratio for all data and for both elements equals 0.994 with a standard error of 0.004. As a result of this, it is statistically not fully proven that there is a systematic difference in accuracy between the two techniques. For the chemical separation of the analytes, a new element-specific resin was used and evaluated. The newer resin was able to remove metals such as Iron, lead, and bismuth better than that traditional strong anion resin, but the uranium fraction obtained using the newer resin contained a larger amount of thorium.