[en] The Oklo phenomenon was identified so soon after its discovery thanks to isotopic analyses of the fission products, especially the rare earths. Subsequently, the laboratory at Cadarache concentrated on the systematic analysis of the many samples collected. Analysis of the Oklo ores necessitated the development of new working procedures for the analysis of rare earths and modifications of the detection system. Separation of the different lanthanides, previously carried out chemically, is now being done in the spectrometer thanks to the reducing action of the rhenium filament: NdO⁺ ions are obtained preferentially instead of Nd⁺ ions, while Sm⁺ ions predominate in the case of Sm. This is one way of avoiding interference of the two elements. For the precise determination of isotopes present in very small concentrations (for example, ¹⁴⁹Sm) the authors increased the sensitivity of the spectrometer by using ''ion counting''. Isotopic determinations of neodymium were made with about a hundred samples; in addition, the authors made fairly many isotopic determinations of samarium and a smaller number of neodymium determinations relative to uranium. Interesting correlations can be derived from the results