The chemical effects of neutron capture have been studied in fulvalenehexacarbonyldimanganese, in order to determine whether or not the ring–ring bond survives nuclear recoil. Retention in the parent form (9.1 %) is comparable to that in other organomanganese compounds, while the radiochemical yield of CpMn(CO)3, the "monomer", is very much lower (0.2%). This suggests that the inter-ring bond is not broken under the conditions in the reaction zone. The formation of radiomanganese compounds with several carbonyl ligands (4.7%) is in accord with mass spectrometric evidence, which suggests that CO may be readily available in the reaction zone.