Neutron-fission competition near threshold: The influence of shells and pairing on the decay of the 241Cm compound nucleus

The excitation functions of the reactions ²³⁸Pu(α, 2n) and ²⁴¹Am(p, 2n), both leading to ²⁴⁰Cm under fission competition, are measured between threshold and 8 MeV excess energy. The two identical excitation functions show a bump-like structure 5 MeV above threshold, which is impossible to explain by the use of statistical reaction theories with standard level density expressions. A compound reaction calculation based on shell dependent level densities for the neutron and fission channels, respectively, with the inclusion of pairing leads to a detailed understanding of the observed structure.