Isotopic analyses by using a sensitive high resolution ion micro-probe (SHRIMP) for natural analogue study of Oklo and Bangombe natural fission reactors

Nd, Sm and U isotopic measurements of four kinds of natural fission reactor samples from Oklo and Bangombe were carried out by using a sensitive high resolution ion micro-probe (SHRIMP). Isotopic data of Nd, Sm and U were obtained within 0.5% of analytical reproducibilities. This precision is enough to detect fission products in micro-regions. The combination of Nd, Sm and U isotopic results provides the determination of nuclear parameters such as neutron fluence, epithermal index and restitution factor of 235U for reactors. If significant amount of fissiogenic Nd has been still preserved in the reactor, the nuclear parameters can be succesfully calculated from the isotopic data. (orig.)