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