Quantifyng Rare Earth Element Content in High Concentrated Samples by ko-NAA

The rare earth elements (REE) are comprised of lanthanide series, from lanthanum to lutetium plus scandium and yttrium. Due to the rising applications of REEs in different fields of technology a lot of attention has been drawn to the extraction of these elements. Therefore, a reliable and accurate characterization technique is required to determine variable levels of REEs starting from mineral matrices all the way to processed samples. The aim of this work is to evaluate the capability of k0-neutron activation analysis (k0-NAA) implemented at Polytechnique Montreal for accurate determination of rare earth elements in high concentrated mineral matrices. Individual factors affecting the measurements including nuclear data used for the calculations, neutron temperature effects, nuclear interferences, spectral interferences, gamma-ray self-attenuation and neutron self-shielding were investigated. Mono rare earth element standard solutions and rare earth oxides were used to investigate these phenomena separately. Several improvements were applied to the current method. Analysis protocols were optimized in terms of irradiation, decay and counting times to obtain accurate results in shorter turnaround times, and uncertainty contributions from aforementioned factors were evaluated. To validate the overall capability of the improved k0-NAA method for REE, a certified reference material (CRM) from Canadian Certified Reference Materials Project (REE-2) with REE content ranging from 7.2 mg kg-1 for Yb to 9610 mg kg-1 for Ce was used. The REE concentration was determined with uncertainty below 7% (at 95% confidence level) and proved to be consistent with the CRM certified concentrations.