Migration of fissiogenic Sm in fractures at the natural fission reactor site of Bangombe and effects of neutron capture on remote samples

The Sm isotopic composition of samples from fractures below the reactor zon e (RZ) Bangombe is investigated by thermal ionization mass spectrometry to shed light on neutron capture effects and migration of fission products. A well-defined mixing line from normal to fissiogenic Sm isotopic composition , which reveals that migration of normal and fissiogenic Sm at the reactor site of Bangombe is more significant than that at other RZs, is found. A small shift in the Sm isotopic composition in one fracture, which was 3 m below the RZ Bangombe, shows neutron capture effects in situ. The shift in dicates a neutron fluence of about 4 x 10(15) neutron/cm(2). The neutron fl uence originates from the fission reaction and is consistent with a macrosc opic neutron capture cross-section. (C) 2001 Elsevier Science B.V. All righ ts reserved.