Neutron activation analysis: a powerful tool for assay of rare-earth elements in terrestrial materials

Neutron activation analysis methods for determination of rare-earth elements in different matrices have been developed at the University of Pavia using the 250 Kw TRIGA Mark II reactor. A critical review of both instrumental and destructive methods is presented, as well as the indication of the best working conditions for irradiation, counting and radiochemical separations. The optimized procedures were utilized in the determination of rare-earth elements in standard reference materials of both mineral and biological origin. The adopted radiochemical procedure is based on the separation of the rare-earth element group by fluoride precipitation. Results, given as the average of six independent determinations and relative standard deviations, are reported and discussed. Precision of the methods can be deduced from the reproducibility of data, whereas accuracy is evaluated by comparison with existing values in the literature. Sensitivity limits under the described operational conditions are also reported, as are trends and correlations among data.