The performance of k(0)-INAA in recent exercises on the certification of rare earth elements in bio-environmental materials

The performance of k(o)-INAA was studied for the determination of the rare earth elements (plus Th and U) in the certification of four new BCR CRM's: 667 Estuarine Sediment, 690 Calcareous Soil, 670 Aquatic Plant and 668 Mussel Tissue. Our results are critically compared with the (later on) certified values, revealing slight discrepancies for the organic matrices aquatic plant and mussel tissue. Although these discrepancies were thought to be associated with the special procedure followed for moisture content determination, no convincing explanation could be found. Mention is also made of problems that are affecting the accuracy and precision of our results, especially with respect to multiplet deconvolution or otherwise troublesome peak fitting, spectral interferences, reaction interferences (notably from U-235-fission) and the non-1/nu thermal cross section behavior. Eventually, detection limits for the REEs (+ Th and U) are calculated in the four materials, allowing to evaluate the applicability of INAA to these types of bio-environmental matrices.