Energy dependence of the nuclear level density below the neutron binding energy

Abstract

The energy spectra of neutrons inelastically scattered from Co, Ag, In, Ta and Au have been measured in the energy range 3.5–8.5 MeV (every 0.5 MeV step) of incident neutrons by means of the time-of-flight technique with pulsed-beam Van de Graaff accelerators and an ion buncher of the Mobley type. The relations between the level density and the excitation energy are obtained in the 2–8 MeV range. The inverse compound nucleus formation cross sections for several forms of the optical model potential are used in the derivation. For Co and Ag, the relations agree with the prediction of the Fermi gas model. For In, Ta and Au, there are obvious breaks in the observed relations at 4–5 MeV excitation. Below the breaks the observed points fit to the curves calculated by the constant temperature model. Above the breaks they fit those based on the Fermi gas or constant temperature model.