The neodymium found at Oklo has a different isotopic composition to that of natural neodymium: the latter contains 27% Nd, while that of Oklo contains less than 6%. The Nd is not produced by fission; the ore contains both fission-produced and natural neodymium. From this Nd content, we can subtract the natural neodymium and gain access to the isotopic composition of neodymium produced by the fission of U. The two isotopes Nd and Nd lead to the formation of Nd and Nd by neutron capture. This excess must be corrected (see above) to obtain agreement between this corrected isotopic composition and that deduced from fission yields.