The Oklo fossil reactor. Determinations of neutron capture cross sections of isotopes occurring in the Oklo phenomenon by irradiation in the reactor Triton

An experimental irradiation of isotopes was carried out in a pool type reactor (Triton reactor) to better the knowledge of capture cross sections of uranium fission products arising in the Oklo phenomenon. Irradiation conditions analysis techniques of samples and methods of calculation to interpret results are described. Capture cross sections of 143Nd, 145Nd, 147Sm, 99Tc, 82Kr, 83Kr, 129Xe, 131Xe were determined will precision and were estimated for dysprosium isotopes and europium isotopes. Found values confirm known data for neodymium and xenon isotopes, but are smaller for 147Sm, 82Kr and 99Tc. These results bring interesting informations in the Oklo phenomenon interpretation. In particular neutron fluence values are confirmed, dating nuclear reactions with the fission neodymium. They give more accurately the ratios water/uranium at the time of nuclear reactions by measurement of spectrum indexes. They explain also the variation, found out before, between reaction duration calculated from plutonium taking part in fissions and the one deduced from the pair 99Tc-99Ru